Lighting apparatus and image pickup apparatus

ABSTRACT

The present invention discloses a lighting apparatus including a light source, an optical member that is placed in front of the light source and provided with a reflecting surface for reflecting light from the light source or prism sections each made up of a refracting surface which receives the light incident from the light source and a reflecting surface for reflecting the light incident from this refracting surface. Here, in the optical member, there is a plurality of pairs of the reflecting surfaces or prism sections arranged in the direction perpendicular to the optical axis within a plane including the radial direction of the light source centered on the optical axis. The present invention can provide a low-profile lighting apparatus using light from the light source with high efficiency.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a lighting apparatus and animage pickup apparatus equipped therewith.

[0003] 2. Description of the Related Art

[0004] A lighting apparatus used for an image pickup apparatus such as afilm camera, digital still camera and video camera is conventionallyconstructed of a light source and optical members such as a reflectorand Fresnel lens that guide a luminous flux generated from this lightsource forward.

[0005] Such a lighting apparatus is available in various designs toefficiently condense the luminous flux irradiated from the light sourcein various directions within a required irradiation field angle.Especially, there is a proposal of placing optical members using totalreflection such as a prism or light guide instead of a Fresnel lensplaced in front of the light source so far and thereby improving lightcondensing efficiency and reducing the size of the apparatus in recentyears.

[0006] An example of this type of proposal described in Japanese PatentLaid-Open No. 2000-250102 is the one using an optical member providedwith a cylindrical lens section having positive refracting property thatcondenses luminous flux emitted from a light source forward and a prismsection that refracts the luminous flux emitted from the light sourcesideward and then leads the luminous flux forward using a totalreflecting surface placed behind. The lighting apparatus according tothe proposal in this Publication makes a light distribution from thecenter of the light source generally uniform by an optical action of theabove-described optical member and then irradiates illuminating lightfrom the same plane of outgoing light. This makes it possible to realizea small-sized illumination optical system with high condensingefficiency.

[0007] Image pickup apparatuses tend to become much smaller and thinnerin recent years than before and there is even a proposal of an extremelythin digital camera such as a card size camera unprecedented by previousarts.

[0008] In line with this, a smaller, thinner light source is also anessential condition and there is a strong demand for making commerciallyfeasible an illumination optical system, which will not deteriorate theoptical performance under such conditions.

[0009] Against such a background, it is also possible to use thelighting apparatus proposed in the above-described Japanese PatentLaid-Open No. 2000-250102 as an ultra-small lighting apparatus.

[0010] However, the lighting apparatus proposed in the above-describedPublication is still thick in the thickness direction and is not thinenough to be housed in a card size camera. For this reason, this cannotbe said as an ideal configuration for a lighting apparatus mounted on acard type camera or card type electronic flash.

SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to provide a highlyefficient lighting apparatus and image pickup apparatus equippedtherewith capable of realizing an extremely thin illumination opticalsystem and providing required optical performance and light distributioncharacteristic.

[0012] In order to attain the above-described object, the lightingapparatus of the present invention includes a light source, an opticalmember which is placed in front of the light source and provided with areflecting surface to reflect light from the light source, characterizedin that the optical member includes a plurality of the reflectingsurface pairs arranged in the direction perpendicular to thelongitudinal direction of the light source on both sides of the opticalaxis.

[0013] Furthermore, the optical member can be provided with a pluralityof prism section pairs made up of a refracting surface that receiveslight incident from the light source and a reflecting surface thatreflects the light incident from the refracting surface arranged in thedirection perpendicular to the longitudinal direction of the lightsource on both sides of the optical axis.

[0014] In the above-described invention, it is possible to form a lenssection having positive refracting power on and close to the opticalaxis on the entrance surface side of the optical member and form theplurality of reflecting surface pairs in the peripheral section.

[0015] Furthermore, in the above-described invention, it is alsopossible to place the edge on the light source side formed byintersection between the refracting surface and the reflecting surfaceof each prism section closer to the light source side for a prismsection which is farther from the optical axis in the directionperpendicular to the longitudinal direction of the light source. In thiscase, it is also possible to place the edges of one out of the pluralityof prism section pairs, farthest from the optical axis in the directionperpendicular to the longitudinal direction of the light source insubstantially the same position as the center position of the lightsource in the direction of the optical axis.

[0016] Furthermore, in the above-described invention, it is alsopossible to include a reflection member which is placed behind the lightsource and which reflects light from the light source toward the opticalmember and allow the reflection member to extend to a position to coverat least part of the reflecting surface of one out of the plurality ofprism section pairs, farthest from the optical axis in the directionperpendicular to the longitudinal direction of the light source.

[0017] Furthermore, in the above-described invention, it is alsopossible to determine the shape of the each reflecting surface in such away that the range of light irradiated through each reflecting surfaceand the range of light irradiated through the lens section practicallyoverlap with each other.

[0018] Furthermore, in the above-described invention, it is alsopossible to make the relation of positions between the light source andthe optical member in the direction of the optical axis changeable.

[0019] Furthermore, in order to attain the above object, the lightingapparatus according to the present invention includes a light source, anoptical member which is placed in front of the light source and areflection member which is placed in such a way as to cover the back ofthe light source and the front space between the light source and theoptical member, and reflects light irradiated from the light sourceforward, characterized in that the optical member includes a lenssection which is placed on and close to the optical axis on the entrancesurface side of the optical member and has positive refracting power anda reflecting section which is placed to the peripheral side of the lenssection, provided closer to the optical axis than the area of thereflection member covering the front space through which the reflectedlight passes, and reflects light from the light source forward.

[0020] In the above-described invention, it is possible to form thereflecting section like a prism having a refracting surface thatreceives light incident from the light source and a reflecting surfacethat reflects light incident from this refracting surface. In this case,it is also possible to construct the refracting surface of thereflecting section with a flat surface whose gradient with respect tothe optical axis is 4° or less. It is also possible to provide a pair ora plurality of the reflecting sections on both sides of the opticalaxis.

[0021] Furthermore, in the above-described invention, it is possible todetermine the shape of the reflecting section in such a way that therange of light irradiated through the reflecting section and the rangeof light irradiated through the lens section and the reflection membersubstantially overlap with each other.

[0022] Furthermore, in the above-described embodiment, it is possible toset an angle α formed by light emitted from the center of the lightsource and incident on the reflecting section with respect to theoptical axis within a range of 20°≦α≦70°.

[0023] Furthermore, in the above-described invention, it is possible tomake the irradiation range variable by changing a relation of positionsbetween the light source and the optical member in the direction of theoptical axis.

[0024] Furthermore, in order to attain the above object, the lightingapparatus according to the present invention includes a light source, anoptical member which is placed in front of the light source and providedwith a lens section having positive refracting power and being placed onand close to the optical axis on the entrance surface side of thisoptical member, a first reflection member which is placed in such a wayas to cover the back of the light source and the front space between thelight source and the optical member and reflects light irradiated fromthe light source forward and a second reflection member which is placedto the peripheral side of the lens section in the vicinity of theentrance surface of the optical member and closer to the optical axisside than the area through which the light reflected by the part of thefirst reflection member covering the front space passes and whichreflects light from the light source forward.

[0025] In the above-described invention, it is possible to provide apair or a plurality of pairs of the second reflection members on bothsides of the optical axis.

[0026] Furthermore, in the above-described invention, it is possible todetermine the shape of the second reflection member in such a way thatthe range of light irradiated through the second reflection member, andthe range of light irradiated through the lens section and the firstreflection member substantially overlap with each other.

[0027] Furthermore, in the above-described invention, it is possible toset an angle α formed by the light emitted from the center of said lightsource and incident on the second reflection member with respect to theoptical axis within a range of 20°≦α≦70°.

[0028] Furthermore, in the above-described invention, it is possible tomake the irradiation range variable by changing a relation of positionsbetween the light source, the optical member and the second reflectionmember in the direction of the optical axis.

[0029] Then, it is possible to mount the lighting apparatus according toeach of the above-described invention on an image pickup apparatus. Inthis case, the image pickup apparatus can have a card-typeconfiguration.

BRIEF DESCRIPTION OF THE DRAWINGS

[0030]FIG. 1 is a longitudinal sectional view of a lighting apparatusaccording to an embodiment of the present invention in the radialdirection of a discharge tube;

[0031]FIG. 2 is a longitudinal sectional view of the lighting apparatusaccording to the embodiment shown in FIG. 1 in the radial direction ofthe discharge tube;

[0032]FIG. 3 is a sectional view of the lighting apparatus according tothe embodiment shown in FIG. 1 in the axial direction of the dischargetube;

[0033]FIG. 4 is an exploded perspective view showing a main opticalsystem of the lighting apparatus according to the embodiment shown inFIG. 1;

[0034]FIG. 5 is a perspective view of a camera equipped with thelighting apparatus according to the embodiment shown in FIG. 1;

[0035]FIG. 6 is a light distribution characteristic diagram of thelighting apparatus according to the embodiment shown in FIG. 1;

[0036]FIG. 7 is a longitudinal sectional view of a lighting apparatus,which is another embodiment of the present invention in the radialdirection of a discharge tube;

[0037]FIG. 8 is a sectional view of the lighting apparatus according tothe embodiment shown in FIG. 7 in the axial direction of the dischargetube;

[0038]FIG. 9 is an exploded perspective view of the main optical systemviewed from the back of the lighting apparatus according to theembodiment shown in FIG. 7;

[0039]FIG. 10 is a longitudinal sectional view of a lighting apparatus,which is another embodiment of the present invention in the radialdirection of a discharge tube;

[0040]FIG. 11 is an exploded perspective view of a main optical systemviewed from the back of a lighting apparatus, which is anotherembodiment of the present invention;

[0041]FIG. 12 is a rear view of the optical member used for the lightingapparatus of the embodiment shown in FIG. 11;

[0042]FIG. 13 is a longitudinal sectional view of a lighting apparatus,which is another embodiment of the present invention on a planeincluding a radial direction of a discharge tube;

[0043]FIG. 14 is a longitudinal sectional view of the lighting apparatusaccording the embodiment shown in FIG. 13 on a plane including theradial direction of the discharge tube;

[0044]FIG. 15 is a sectional view of the lighting apparatus accordingthe embodiment shown in FIG. 13 in the longitudinal direction of thedischarge tube;

[0045]FIG. 16 is an exploded perspective view of the lighting apparatusaccording the embodiment shown in FIG. 13;

[0046]FIG. 17 is a perspective view of the lighting apparatus accordingthe embodiment shown in FIG. 13 viewed from the back;

[0047]FIG. 18 is a perspective view of a camera equipped with thelighting apparatus according the embodiment shown in FIG. 13;

[0048]FIG. 19 is a longitudinal sectional view of a lighting apparatus,which is another embodiment of the present invention in the radialdirection of a discharge tube;

[0049]FIG. 20 is a longitudinal sectional view of the lighting apparatusaccording to the embodiment shown in FIG. 19 in the radial direction ofthe discharge tube;

[0050]FIG. 21 is a longitudinal sectional view of a lighting apparatus,which is another embodiment of the present invention in the radialdirection of a discharge tube;

[0051]FIG. 22 is a longitudinal sectional view of the lighting apparatusaccording to the embodiment shown in FIG. 21 in the radial direction ofthe discharge tube;

[0052]FIG. 23 is an exploded perspective view of the lighting apparatusaccording to the embodiment shown in FIG. 21;

[0053]FIG. 24 is a sectional view of a lighting apparatus (in acondensed state), which is another embodiment of the present inventionin the radial direction of a discharge tube;

[0054]FIG. 25 is a sectional view of the lighting apparatus (in adiffused state) in FIG. 24 in the radial direction of the discharge tubeand a traced drawing of representative light beams;

[0055]FIG. 26 is a sectional view of the lighting apparatus in FIG. 24cut with a plane including the center axis of the discharge tube;

[0056]FIG. 27 is an exploded perspective view of the optical system ofthe lighting apparatus in FIG. 24;

[0057]FIG. 28 is a perspective view of (a) compact camera and (b)cardsize camera equipped with the lighting apparatus in FIG. 24;

[0058]FIG. 29 is a light distribution characteristic diagram of thelighting apparatus (in a condensed state) in FIG. 24;

[0059]FIG. 30 is a light distribution characteristic diagram of thelighting apparatus (in a diffused state) in FIG. 24;

[0060]FIG. 31 is a sectional view of a lighting apparatus (in acondensed state), which is another embodiment of the present inventionin the radial direction of a discharge tube;

[0061]FIG. 32 is a sectional view of the lighting apparatus (in adiffused state) in FIG. 31 in the radial direction of the discharge tubeand a traced drawing of representative light beams;

[0062]FIG. 33 is a sectional view of the lighting apparatus in FIG. 31cut with a plane including the center axis of the discharge tube;

[0063]FIG. 34 is an exploded perspective view of the optical system ofthe lighting apparatus in FIG. 31;

[0064]FIG. 35 is a sectional view of a lighting apparatus (in acondensed state), which is another embodiment of the present inventionin the radial direction of a discharge tube;

[0065]FIG. 36 is a sectional view of the lighting apparatus (in adiffused state) in FIG. 35 in the radial direction of the discharge tubeand a traced drawing of representative light beams;

[0066]FIG. 37 is a sectional view of a lighting apparatus (in acondensed state), which is another embodiment of the present inventionin the radial direction of a discharge tube;

[0067]FIG. 38 is a sectional view of the lighting apparatus (in adiffused state) in FIG. 37 in the radial direction of the discharge tubeand a traced drawing of representative light beams;

[0068]FIG. 39 is an exploded perspective view of an optical system of alighting apparatus, which is another embodiment of the presentinvention; and

[0069]FIG. 40 is a rear view of the optical member making up thelighting apparatus in FIG. 39.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0070]FIG. 1 to FIG. 5 show a camera lighting apparatus, which is anembodiment of the present invention. FIG. 1 and FIG. 2 are sectionalviews of main members of the optical system of the above-describedlighting apparatus on a plane including the radial direction of adischarge tube and the vertical direction (direction perpendicular tothe optical axis) of this plane is the direction perpendicular to thelongitudinal direction of the discharge tube (light source). FIG. 3 is asectional view of the above-described lighting apparatus cut with ahorizontal plane including the center axis of the discharge tube makingup the optical system. FIG. 4 is an exploded perspective view showingthe main optical system of the above-described lighting apparatus andFIG. 5 is a perspective view of a camera equipped with theabove-described lighting apparatus.

[0071]FIG. 1 to FIG. 3 also show traced drawings of representative lightbeams emitted from the center of the discharge tube, which is the lightsource, and especially FIG. 1(a), 1(b) and FIG. 2(a), 2(b) show theluminous flux emitted from the center of the light source on the samesection segmentized according to the position of the incident light.

[0072]FIG. 5(a) shows a compact camera and FIG. 5(b) shows a card typecamera. In these figures, reference numeral 11 denotes the body of thecamera and reference numeral 1 denotes a lighting apparatus placed atthe top of the body of the camera 11. Reference numeral 12 denotespicture-taking lens and reference numeral 13 denotes a shutter releasebutton.

[0073] In FIG. 5(a), reference numeral 14 denotes an operation member tozoom the picture-taking lens 12 and depressing this operation member 14frontward allows an image to zoom in and depressing this operationmember 14 backward allows an image to zoom out.

[0074] Furthermore, reference numeral 15 denotes a mode setting buttonto switch between various modes of the camera and reference numeral 16denotes a liquid crystal display window to inform the user of theoperation of the camera.

[0075] In FIG. 5(a) and 5(b), reference numeral 17 denotes a lightreceiving window of a photometer to measure the brightness of externallight and reference numeral 18 denotes an inspection window of a finder.

[0076] Then, the members that determine an optical characteristic of thelighting apparatus will be explained in detail using FIG. 1 to FIG. 4.

[0077] In these figures, reference numeral 2 denotes a cylindricaldischarge tube (xenon tube). Reference numeral 3 denotes a reflectorthat reflects forward the member of the luminous flux emitted from thedischarge tube 2 and directed backward in the direction of theirradiation optical axis. This reflector 3 has a high-reflectance innersurface made of a metallic material such as radiant aluminum, or is madeof a resin material having an inner surface on which a high-reflectancemetal-evaporated surface is formed.

[0078] Reference numeral 4 denotes a prism-like one-piece optical memberand on the entrance surface of light from the discharge tube 2, there isa plurality of prism section pairs P made up of refracting surfaces 4 b,4 d, 4 f, 4 b′, 4 d′, 4 f′ having refracting power in the directionperpendicular to the longitudinal direction of the discharge tube 2 andreflecting surfaces 4 c, 4 e, 4 g, 4 c′, 4 e′, 4 g′ that almost satisfya total reflection condition for the light incident from theserefracting surfaces arranged in the direction perpendicular to thelongitudinal direction of the above-described discharge tube 2 on bothsides of the optical axis L.

[0079] Furthermore, as shown in FIG. 3, on the plane of outgoing lightof the optical member 4 is a prism array 4 h having refracting power inthe longitudinal direction of the discharge tube 2. As the material ofthe optical member 4, a high transmittance optical resin material suchas acrylic resin or glass material is suitable.

[0080] In the above-described configuration, in the case where thecamera is set, for example, to “electronic flash auto mode”, after theshutter release button 13 is pressed by the user, a control circuit (notshown) decides whether light should be emitted from the lightingapparatus 11 or not based on the brightness of external light measuredby a photometer (not shown), sensitivity of the film loaded or thecharacteristic of an image pickup device such as a CCD or CMOS.

[0081] When the control circuit decides that “light should be emittedfrom the lighting apparatus”, the control circuit outputs alight-emitting signal and allows the discharge tube 2 to emit lightthrough a trigger lead wire attached to the reflector 3.

[0082] Of the luminous flux emitted from the discharge tube 2, theluminous flux component emitted backward in the direction of theirradiation optical axis L enters the optical member 4 placed in frontof the discharge tube 2 through the reflector 3 and the luminous fluxcomponent emitted forward in the direction of the irradiation opticalaxis directly enters the optical member 4. These both luminous fluxcomponents are changed to luminous flux having a predetermined lightdistribution characteristic through the optical member 4 and thenirradiated onto an object.

[0083] Hereafter, in the above-described lighting apparatus 11, asetting of an optimal shape to keep the light distributioncharacteristic uniform within the required irradiation range whilesignificantly slimming the overall shape of the lighting optical systemin particular will be explained using FIG. 1 to FIG. 3.

[0084] First, a basic concept for optimizing the light distributioncharacteristic in the direction perpendicular to the longitudinaldirection (vertical direction) of the discharge tube 2 will be explainedusing FIG. 1 and 2. All FIG. 1(a), 1(b) and FIG. 2(a), 2(b) show thesame section and show different light beam tracing lines in differentcases.

[0085] These figures show inner and outer diameters of the glass tubemaking up the discharge tube 2. In an actual light-emitting phenomenonof this type of discharge tube, light is often emitted from the fullinner diameter to improve the efficiency and it is reasonable toconsider that light is emitted virtually uniformly from light-emittingpoints across the full inner diameter of the discharge tube 2. However,for simplicity of explanation, suppose the luminous flux emitted fromthe center of the discharge tube 2 is representative luminous flux andthe figures only show luminous flux emitted from the center of thedischarge tube 2.

[0086] As an actual light distribution characteristic, the lightdistribution characteristic as a whole changes in a direction in whichluminous flux spreads slightly due to luminous flux emitted from theperiphery of the discharge tube 2 in addition to the representativeluminous flux as shown in the figures, but this luminous flux has almostan identical tendency of light distribution characteristic, andtherefore the following explanations will be based on thisrepresentative luminous flux.

[0087] First, the characteristic shape of the optical system of theabove-described lighting apparatus will be explained one by one. Theshape of the back of the reflector 3 in the direction of the irradiationoptical axis is semi-cylindrical (hereinafter referred to as“semi-cylindrical section 3 a”) almost concentric with the dischargetube 2. This is a shape, which is effective to return the reflectedlight at the reflector 3 to close to the center of the discharge tube 2again, and has the effect of preventing adverse influences fromrefractions of the glass part of the discharge tube 2.

[0088] Furthermore, such a configuration makes it possible to handle thelight reflected by the reflector 3 as the outgoing light almostequivalent to the direct light from the discharge tube 2, and therebyreduce the size of the entire optical system. Furthermore, the reasonthat the reflector 3 has a semi-cylindrical shape is that having a sizesmaller than this will require the size of the optical member 4 to beincreased to condense sideward luminous flux, while having a size largerthan this will increase luminous flux trapped inside the reflector 3,resulting in a reduction of efficiency.

[0089] On the other hand, the upper and lower peripheral sections of thereflector 3 are shaped (hereinafter referred to as “curved surfacesection 3 b, 3 b′”) so as to cover the back of the reflecting surfaces 4g and 4 g′ placed in such a way that the boundary edge E between therefracting surfaces 4 f and 4 f′ of the outermost prism section in thevertical direction of the prism sections P of the optical member 4 andthe reflecting surface 4 g and 4 g′ is located at almost the sameposition as the center of the discharge tube 2 in the direction of lightaxis.

[0090] This is because, the luminous flux emitted from the center of thedischarge tube 2 can be ideally reflected (totally reflected) by thereflecting surfaces 4 g and 4 g′ as shown in FIG. 2(b), whereas some ofthe luminous flux emitted from the front side of the discharge tube 2(left to the center of the discharge tube 2 in the figure), especiallywhen the discharge tube 2 has a large inner diameter, cannot satisfy thetotal reflection condition on the reflecting surfaces 4 g and 4 g′ andcannot be totally reflected, thereby including a luminous flux componentthat goes out of the reflecting surfaces 4 g and 4 g′. It is for thisreason that the above-described shape is adopted for the reflector 3 inorder to effectively use this luminous flux.

[0091] In this way, by extending the shape of the reflector 3 over theupper and lower sides of the optical member 4 along the shapes of thereflecting surfaces 4 g and 4 g′ as shown in the figure, it is possibleto allow the luminous flux which cannot be totally reflected by thereflecting surfaces 4 g and 4 g′ and which goes out of the reflectingsurfaces 4 g and 4 g′, to reenter the optical member 4 and also lead thereflected luminous flux to within a predetermined irradiation rangeefficiency.

[0092] Then, the shape of the optical member 4 that has the largestinfluence on the light distribution characteristic of theabove-described lighting apparatus 11 will be explained. In order forthe optical member 4 to obtain a light distribution capable of uniformlyilluminating the required irradiation range with the thinnest shape inthe direction of the optical axis, this embodiment determines the shapesof its members as follows.

[0093] As shown FIG. 1(a), the luminous flux emitted from the dischargetube 2 toward the vicinity of the irradiarion optical axis passesthrough a cylindrical lens surface 4 a formed in the central area (thearea is placed on and close to the optical axis L. In other words, theoptical axis L passes through the area.) of the entrance surface of theoptical member 4 that gives positive refracting power, is changed to aluminous flux having a uniform light distribution characteristic withina predetermined angle range and then goes out of the exit surface 4 h.

[0094] Here, in order to provide a uniform light distributioncharacteristic, the cylindrical lens surface 4 a of this embodiment isconstructed to have a continuous non-spherical shape so that the angleof the light going out of the center of the discharge tube 2 isproportional to the angle of the light going out of the cylindrical lenssurface 4 a and the light is condensed at a certain rate.

[0095] Then, the luminous flux component shown in FIG. 1(b), that is,the luminous flux component emitted from the center of the dischargetube 2 upward and downward at a slightly greater angle than that of theluminous flux component shown in FIG. 1(a) above (however, the figurewill show only the luminous flux component emitted downward hereafter)will be explained.

[0096] This luminous flux component is refracted through firstrefracting surfaces 4 b and 4 b′ made up of flat surfaces, enters intothe prism section P and then most of the luminous flux component istotally reflected by the first reflecting surfaces 4 c and 4 c′ made upof predetermined curved surfaces and changed to a luminous flux having alight distribution characteristic almost equivalent to the irradiationangle distribution in FIG. 1(a).

[0097] Here, the angle range of the luminous flux component incident onthe refracting surfaces 4 b and 4 b′ is much narrow than the incidentangle range of the luminous flux component shown in FIG. 1(a). For thisreason, fitting the above-described member within the irradiation anglerange shown in FIG. 1(a) requires the first reflecting surfaces 4 c and4 c′ to be shaped so that the angle range of the luminous flux is spreadconsiderably at a certain rate. Optimizing the shapes of the firstreflecting surfaces 4 c and 4 c′ based on this concept makes it possibleto almost match the resulting irradiation angle range as shown in thefigure with the irradiation range shown in above-described FIG. 1(a).

[0098] Furthermore, as shown in FIG. 2(a), the luminous flux componentwhich is emitted from the center of the discharge tube 2 upward anddownward at a greater angle than that of the luminous flux component ofabove-described FIG. 1(b) is refracted through the second refractingsurfaces 4 d and 4 d′ made up of flat surfaces, enters into the prismsection P, and most of the luminous flux is totally reflected by thesecond reflecting surfaces 4 e and 4 e′ made up of predetermined curvedsurfaces and changed to a luminous flux with a uniform lightdistribution characteristic almost equivalent to the irradiation angledistribution in above-described FIG. 1(a) and 1(b).

[0099] Even in this case, the angle range of the luminous flux incidenton the second refracting surfaces 4 d and 4 d′ is much narrower rangethan the angle range of the luminous flux shown in FIG. 1(a) as in thecase of FIG. 1(b), and fitting the above-described luminous fluxcomponent within the irradiation angle range shown in FIG. 1(a) requiresthe second reflecting surfaces 4 e and 4 e′ to be shaped so that theangle range of the luminous flux is spread considerably at a certainrate. Optimizing the shapes of the second reflecting surfaces 4 e and 4e′ based on this concept makes it possible to almost match the resultingirradiation angle range as shown in the figure with the irradiationrange shown in above-described FIG. 1(a).

[0100] Furthermore, as shown FIG. 2(b), the luminous flux componentemitted from the discharge tube 2 upward or downward at the greatestirradiation angle is refracted through the third incident surfaces 4 fand 4 f′ made up of flat surfaces, enters into the prism section P, andmost of the luminous flux is totally reflected by the third reflectingsurfaces 4 g and 4 g′ made up of predetermined curved surfaces, changedto a luminous flux having a uniform light distribution characteristicalmost equivalent to the irradiation angle distribution inabove-described FIG. 1(a), 1(b) and 1(c) and then goes out of the plane4 h.

[0101] Thus, in the sections shown in FIG. 1 and FIG. 2, all theluminous flux emitted from the center of the discharge tube 2 aredivided into luminous flux components of a total of 7 areas by opticalactions of the cylindrical surface 4 a and 6 pairs of refractingsurfaces and reflecting surfaces in FIG. 1(a). However the irradiationangle ranges of the luminous flux components of these areas overlap witheach other and form a uniform light distribution on the irradiationsurface.

[0102] Thus, segmentizing the shapes of the first to third reflectingsurfaces into smaller portions than the conventional arts makes itpossible to obtain effects specific to this embodiment unprecedented bythe conventional arts.

[0103] First, the reflecting surfaces are not placed continuously in thedirection of the optical axis as in the cases of the conventional arts,but placed discretely and a plurality of reflecting surface layers isplaced in the vertical direction perpendicular to the irradiationoptical axis L in such a way as to overlap one another, which makes itpossible to significantly reduce the thickness of the lighting opticalsystem in the vertical direction including the optical member 4.

[0104] That is, placing the first reflecting surfaces 4 c and 4 c′outside the cylindrical lens surface 4 a symmetrically in the verticaldirection, placing the second reflecting surfaces 4 e and 4 e′symmetrically in the vertical direction outside the area of thereflecting surfaces 4 c and 4 c′ where the positions in the direction ofthe optical axis overlap one another and placing the third reflectingsurfaces 4 g and 4 g′ symmetrically in the vertical direction outsidethe areas of the above-described two reflecting surfaces 4 c, 4 c′, 4 eand 4 e′ where the positions in the direction of the optical axisoverlap one another makes it possible to reduce the thickness of thereflecting surface as a whole in the direction of the optical axis to ahalf or less. By adopting such arrangement, this embodiment makes itpossible to construct a lighting optical system capable of obtaining apredetermined light distribution characteristic with a thickness assmall as approximately 4 mm.

[0105] Second, constructing a plurality of surfaces having total reflexaction can prevent the problem of a conventional light guide typeelectronic flash, that is, the problem that when an optical membergenerally made of a resin optical material is placed close to a lightsource, the optical member is melted by heat produced by the lightsource and it is impossible to obtain the original opticalcharacteristic depending on the light-emitting condition.

[0106] That is, by constructing the reflecting surface with a pluralityof layers, it is possible to place the edge E, which is a boundarybetween the refracting surface and reflecting surface of the opticalmember 4 which is most vulnerable to heat, away from the light source,minimize the influence of radiant heat and convection heat producedduring continuous light emission on the optical resin material andprevent deterioration of the optical characteristic.

[0107] Third, it is possible to construct a lighting optical system,which is small but with little efficiency deterioration. That is, sincethe reflecting surface is basically constructed as a surface with totalreflex action, there is little efficiency deterioration, there is alsofewer luminous flux components emitted from other than the center of thelight source whose irradiation direction drastically changes thusproviding high efficiency.

[0108] Furthermore, the reflector 3 is constructed of three parts of asemi-cylindrical section 3 a, curved surface sections 3 b and 3 b′ andflat surface sections 3 c and 3 c′ and the flat surface sections 3 c and3 c′ constitute reflectors capable of effectively utilizing luminousflux by reflecting the luminous flux components emitted from the front(left side in the figure) of the center of the light source and directeddiagonally backward. Thus, constructing this surface with a flat surfacemakes it possible to efficiently irradiate light within the requiredirradiation angle range of luminous flux emitted from other than thecenter.

[0109] Thus, it is possible to construct a small and highly efficientlighting optical system with little loss of light quantity to theoutside of the required irradiation range using only a small number ofmembers of the reflector 3 and optical member 4.

[0110] Then, a condensing action in the longitudinal direction of thedischarge tube 2 according to this embodiment will be explained usingFIG. 3.

[0111]FIG. 3 is a sectional view of the discharge tube 2 cut with aplane including the center axis accompanied by a traced drawing of lightbeams from the center of the light source. As shown in the figure, theexit surface of the optical member 4 is constructed of a prism array 4 hhaving two slopes of the same angle formed in the central area andFresnel lens sections 4 i and 4 i′ formed in the peripheral sections.

[0112] This embodiment sets a constant angle of 105° as the apex angleof each of the prism array 4 h in the central area. The prism array 4 hwith such an angle setting has the effect of allowing luminous fluxcomponents with a relatively large angle of incidence (luminous fluxcomponents with the angle of incidence on the optical member 4 ranging30° to 40°) to go out of the exit surface with the same angle at whichlight is refracted through the entrance surface, that is, allowingluminous flux components to go out of the exit surface without beingaffected by refraction on the exit surface, having the effect ofcondensing incident luminous flux as luminous flux within a certainrange of irradiation angles.

[0113] This embodiment shows an example where the apex angle of thisprism array 4 h is set to 105°, but the angle setting is not limited tothis, and setting an angle smaller than this angle, for example, 90°makes it possible to set a narrower irradiation angle for luminous fluxemitted from the optical member 4, and on the contrary, setting an anglegreater than this angle, for example, 120° makes it possible to set awider irradiation angle for luminous flux emitted from the opticalmember 4.

[0114] On the other hand, as shown in FIG. 3, there are also someoutgoing luminous flux components, which are totally reflected by thisprism array 4 h and returned to the discharge tube 2 again. Thisluminous flux component is reflected by the reflector 3 and entered intothe optical member 4 again, changed to a predetermined angle member bythe prism array 4 h and then irradiated onto an object.

[0115] Thus, most of luminous flux emitted from the center of thedischarge tube 2 is changed to luminous flux with a certain angledistribution and irradiate out of the optical member 4. In this case,the light distribution is solely dependent on the angle setting of theprism array 4 h and is not affected by the pitch, etc. of the prismarray 4 h, and therefore allows condensing control in an extremelyshallow area without the need for the depth in the direction of theoptical axis. Therefore, this makes it possible to drastically reducethe overall size of the lighting optical system.

[0116] Furthermore, as shown in the figure, Fresnel lens sections 4 iand 4 i′ are formed on the exit surface on the periphery of the opticalmember 4. Though the optical member 4 is considerably thin, there is anarea in this peripheral section where luminous flux with certaindirectivity is obtained and forming the Fresnel lens in this area allowsrelatively efficient condensing action.

[0117] In the figure, no conspicuous condensing operation in thisportion is observable. This is because only luminous flux emitted fromthe center of the discharge tube 2 is shown and most of luminous fluxemitted from around the end of the discharge tube 2 is changed tomembers that concentrate on the irradiation optical axis L.

[0118] Thus, determining the shape of the exit surface of each sectionof the optical member 4 allows even an extremely thin lighting opticalsystem placed near the discharge tube 2 to condense luminous flux withina certain angle range efficiently.

[0119]FIG. 6 shows an actual light distribution characteristic diagramobtained in the optical system configuration in this embodiment. Asshown in the figure, this embodiment can obtain a uniform lightdistribution characteristic within a certain angle range and obtain acharacteristic of an ideal lighting optical system in which almost nolight is irradiated outside the required irradiation angle range.

[0120] Thus, this embodiment performs condensing control for thelongitudinal direction of the discharge tube 2 using the prism array 4 hand Fresnel lens sections 4 i and 4 i′ on the side of the exit surfaceof the optical member 4 and performs efficient condensing control forthe direction quasi-perpendicular (vertical direction) to thelongitudinal direction of the discharge tube 2 using the cylindricallens surface 4 a and a plurality of pairs of reflecting surfaces 4 c, 4e, 4 g, 4 c′, 4 e′ and 4 g′ placed on the side of the entrance surfaceof the optical member 4. This provides an ultra-thin lighting opticalsystem with an excellent optical characteristic unprecedented by theprevious arts.

[0121] This embodiment has described the case where light distributioncontrol with respect to the direction quasi-perpendicular (verticaldirection) to the longitudinal direction of the discharge tube 2 is setin such a way as to obtain a quasi-identical light distribution to becontrolled by the cylindrical lens surface 4 a and a plurality of pairsof reflecting surface 4 c, 4 e, 4 g, 4 c′, 4 e′ and 4 g′ placed on theside of the entrance surface of the optical member 4. However, lightdistribution control is not limited to this embodiment, but differentlight distributions may also be used in the case where the light sourcehas a size of a certain value or greater.

[0122] That is, the irradiation angle of a cylindrical lens surfaceclose to the light source tends to spread considerably when the lightsource is quite large. On the other hand, when the reflecting surface islocated farthest from the light source, the degree of condensing doesnot deteriorate even if the size of the light source increases to acertain degree, providing a distribution not quite different from theinitially set irradiation angle distribution.

[0123] Thus, the cylindrical lens surface whose control surface is closeto the light source is set so that the distribution of luminous fluxemitted from the center of the light source becomes narrower than apredetermined desired light distribution.

[0124] Likewise, it is desirable to set a light distribution afterreflection for each reflecting surface according to the position fromthe center of the light source one by one instead of setting ancoincidental light distribution uniformly.

[0125] That is, it is desirable to preset a reflecting surface close tothe light source so that the angle distribution of luminous flux fromthe center of the light source becomes narrower and preset a reflectingsurface away from the light source so that the angle distribution ofluminous flux from the center of the light source has a desired lightdistribution characteristic in the case where this lighting opticalsystem is applied to a light source having a certain finite size whichis negligible.

[0126] Furthermore, this embodiment has described the case where eachsurface configuration on the entrance surface and each surfaceconfiguration on the exit surface of the optical member 4 are symmetricwith respect to the optical axis, but this embodiment is not limited tosuch a symmetric shape.

[0127] In this embodiment, the optical member 4 is constructed of threelayers of reflecting surfaces on both sides of the optical axis, but theoptical member 4 need not always be constructed of the same number oflayers of reflecting surfaces. For example, two layers of reflectingsurfaces are provided on the upper side and three layers of reflectingsurfaces are provided on the lower side. The two layers in the upper andlower sides form a pair in this case, too.

[0128] Likewise, with respect to the prism array 4 h formed in thecentral area on the exit surface of the optical member 4, it is alsopossible to use prisms having different angle settings for the right andleft sides to provide variations in the light distributioncharacteristic in right and left directions. Moreover, with respect tothe Fresnel lens sections 4 i and 4 i′ in the peripheral section, it isalso possible to provide variations in the degree of condensing toprovide variations in the overall light distribution characteristic.

[0129]FIG. 7 to FIG. 9 show the lighting apparatus, which is anotherembodiment of the present invention. FIG. 7(a) is a sectional view ofmain members of the optical system of the above-described lightingapparatus cut with a plane including the radial direction of thedischarge tube and FIG. 7(B) in which the vertical direction (directionperpendicular to the optical axis) on this plane is the directionperpendicular to the longitudinal direction of the discharge tube (lightsource) adds a traced drawing of light beams from the center of thelight source to the sectional view in FIG. 7(a). Furthermore, FIG. 8 isa sectional view of the optical system of the above-described lightingapparatus cut with a plane passing through the axis of the dischargetube in the longitudinal direction and FIG. 9 is a perspective viewshowing the above-described lighting apparatus.

[0130] In these figures, reference numeral 22 denotes a discharge tube(xenon tube) and reference numeral 23 denotes a reflector. Thisreflector 23 has almost the same function as that of the above-describedembodiment. However, as shown in FIG. 8 and FIG. 9, both sides 23 a and23 a′ of the reflector 23 have shapes extending straight forward inparallel to the optical axis L.

[0131] Reference numeral 24 denotes a prism-like one-piece opticalmember and on the plane of the light incident from the discharge tube22, there is a plurality of prism section pairs P made up of refractingsurfaces 24 b, 24 d, 24 b′ and 24 d′ having refracting power in thedirection quasi-perpendicular to the longitudinal direction of thedischarge tube 22 and reflecting surfaces 24 c, 24 e, 24 c′ and 24 e′that almost satisfy a total reflection condition for the light incidentfrom these refracting surfaces arranged in the above-describedquasi-perpendicular direction on both sides of the optical axis L.

[0132] Furthermore, as shown in FIG. 8, on the side of the exit surfaceof the optical member 24, there is a prism array 24 h having refractingpower in the longitudinal direction of the discharge tube 22. As thematerial of the optical member 24, a high transmittance optical resinmaterial such as acrylic resin or glass material is suitable as in thecase of the first embodiment.

[0133] The lighting apparatus according to this embodiment is intendedto make the overall shape of the lighting optical system extremely thin,narrow the irradiation range of illumination light most and reduce thewidth of the opening in the longitudinal direction of the discharge tube22 to realize miniaturization. The method of determining this optimalshape will be explained using FIG. 7 and FIG. 8 below.

[0134]FIG. 7 shows a longitudinal sectional view of the above-describedlighting apparatus cut in the radial direction of the discharge tube 22and shows a basic concept for narrowing the light distributioncharacteristic in the vertical direction to a small irradiation anglerange.

[0135]FIG. 7(b) shows the same section as that of FIG. 7(a) with only alight beam tracing lines added.

[0136] In the same figure, the inner and outer diameters of the glasstube as the discharge tube 22 are shown. In the same way as for theabove-described embodiment, the luminous flux emitted from the center ofthe discharge tube 22 is regarded as the representative luminous fluxand the figures only show luminous flux emitted from the center of thedischarge tube 22. As an actual light distribution characteristic, thelight distribution characteristic as a whole changes in a slightlyspreading direction due to luminous flux emitted from the periphery ofthe discharge tube 22 in addition to the representative luminous flux asshown in the figures, but this luminous flux has almost an identicaltendency of light distribution characteristic, and therefore thefollowing explanations will be based on this representative luminousflux.

[0137] First, the shapes of the optical system of the above-describedlighting apparatus will be explained one by one. With respect to thissection, the shape of the back of the reflector 23 in the direction ofthe irradiation optical axis L is semi-cylindrical (hereinafter referredto as “semi-cylindrical section 23 a”) almost concentric with thedischarge tube 22 for the same reason described in the above-describedembodiment and includes curved surface sections 23 b and 23 b′ coveringthe back of the outermost reflecting surfaces 24 e and 24 e′ in thevertical direction of the optical member 24 and the flat surfacesections 23 c and 23 c′ connecting these curved surface sections 23 band 23 b′ and semi-cylindrical section 23 a.

[0138] Then, the shape of the optical member 24 will be explained. Inorder to construct an optical system with the thinnest shape in thedirection of the optical axis and the narrowest irradiation angle, thatis, an optical system with the highest condensing performance, thisembodiment determines the shape of each section of the optical member 24as follows.

[0139] First, as shown in FIG. 7(a), the optical member 24 isconstructed of a plurality of reflecting surfaces having total reflexaction on most of light incident from each refracting surface as in thecase of the above-described embodiment. However, it is different fromthe optical member 4 of the above-described embodiment in thatreflecting surfaces 24 c, 24 e, 24 c′ and 24 e′ are formed two layerseach in such a way as to be symmetrical with respect to the optical axisL in the vertical direction. The boundary edge E between the refractingsurface and reflecting surface in the outermost prism section P in thevertical direction is located at almost the same position as the centerof the discharge tube 22 in the direction of the optical axis L.

[0140] Here, the number of split reflecting surfaces (number of layers)is reduced because each reflecting surface needs to be non-spherical toobtain a precise light distribution and taking into account the factthat providing a plurality of such complicated non-spherical shapes islikely to further complicate the configuration of die manufacturing.

[0141] Thus, forming at least two layers of reflecting surface on bothsides of the optical axis in the optical member will make the opticalmember, and therefore the lighting apparatus thinner.

[0142] The optical member 24 consists of the following sections, whichwill be explained below. First, a cylindrical lens surface 24 a isformed in the central area through which the irradiation optical axis Lpasses and prism sections P including first refracting surfaces 24 b and24 b′ and first reflecting surfaces 24 c and 24 c′ are formedsymmetrically with respect to the vertical direction on both sides ofthe optical axis L outside the cylindrical lens surface 24 a.

[0143] Outside these prism sections P, other prism sections P includingsecond refracting surfaces 24 d and 24 d′, and second reflectingsurfaces 24 e and 24 e′ are formed symmetrically with respect to thevertical direction on both sides of the optical axis L. Furthermore, aprism array 24 h made up of a plurality of prisms is formed on the exitsurface.

[0144] An optical action of the optical member 24 having such a shapewill be explained using the light traced drawing in FIG. 7(b).

[0145] First, the luminous flux toward the vicinity of the irradiationoptical axis L passes through the cylindrical lens surface 24 a givingpositive refracting power formed on the entrance surface of the opticalmember 24, is changed to a luminous flux parallel to the optical axiswith respect to this section and then goes out of the exit surface(prism array 24 h).

[0146] Then, the luminous flux component emitted from the center of thedischarge tube 22 upward or downward at a relatively large angle isrefracted through the first refracting surfaces 24 b and 24 b′ made upof flat surfaces, enters into the prism section P, and most of theluminous flux is totally reflected by the first reflecting surfaces 24 cand 24 c′ made up of a predetermined curved surface and changed to aluminous flux parallel to the optical axis L with respect to thissection and then goes out of the exit surface (prism array 24 h).

[0147] Furthermore, the luminous flux component emitted from the centerof the discharge tube 22 upward or downward at a greater irradiationangle is refracted through the second diffraction surfaces 24 d and 24d′ made up of flat surfaces, entered into the prism section P, and mostof the luminous flux is totally reflected by the second reflectingsurfaces 24 e and 24 e′ made up of predetermined curved surfaces,changed to a luminous flux parallel to the optical axis L with respectto this section and then goes out of the exit surface (prism array 24h).

[0148] Thus, the luminous flux emitted from the center of the dischargetube 22 is split into luminous flux components of a total of five areasby an optical action of the cylindrical surface 24 a and the fourrefracting surfaces and reflecting surfaces and luminous flux of allareas is changed to luminous flux parallel to the optical axis withrespect to this section. This provides a light distribution with anarrow irradiation range and high condensing performance.

[0149] Thus, segmentizing the reflecting surfaces provided for theoptical member 24 into smaller portions than the conventional arts makesit possible to further reduce the thickness of the optical member 24 asin the case of the above-described embodiment. Furthermore, since theedge E, which is a boundary between the refracting surface andreflecting surface, is placed away from the center of the discharge tube22, it is possible to prevent deterioration of the opticalcharacteristic of the optical resin material due to the influence ofradiant heat from the light source.

[0150] Then, the shape of the lighting apparatus in the longitudinaldirection of the discharge tube 22 according to this embodiment will beexplained using FIG. 8.

[0151]FIG. 8 is a sectional view of the lighting apparatus cut with aplane including the center axis of the discharge tube 22. As shown inthe figure, the exit surface of the optical member 24 is constructed ofa prism array 24 h made up of a plurality of prisms having two slopes ofthe same angle. The condensing effect using this prism array 24 h isalmost the same as that of the above-described embodiment.

[0152] This embodiment, in this sectional view, is characterized in thatboth sides 23 a and 23 a′ of the reflector 23 extend forward inquasi-parallel to the optical axis L and that the entire exit surface ofthe optical member 24 is constructed of the prism array 24 h.

[0153] This is a configuration intended to convert luminous fluxincident on the entire prism surface on the exit surface of the opticalmember 24 to luminous flux having a uniform angle component independentof locations.

[0154] That is, this configuration is intended not only to preventluminous flux from going out of a large opening which exists on the sideof the optical member 24 by allowing the sides 23 a and 23 a′ of thereflector 23 to extend forward in quasi-parallel to the optical axis butalso to prevent light incident on the prism array 24 h of the opticalmember 24 from having directivity and make all luminous flux enter theprism array 24 h placed on the front of the optical member 24 under thesame condition by returning the reflected luminous flux to the dischargetube 22 side at the same angle as the angle of incidence.

[0155] Thus, it is possible to provide a thin-shaped lighting opticalsystem with unprecedentedly high directivity by performing condensingcontrol using the prism array 24 h on the side of the exit surface ofthe optical member 24 for the longitudinal direction of the dischargetube 22 and performing efficient condensing control through refractionsby the cylindrical lens surface 24 a provided on the discharge tube 22side and reflections by a plurality of pairs of reflecting surfaces 24c, 24 e, 24 c′ and 24 e′ for the direction quasi-perpendicular to thelongitudinal direction (vertical direction) of the discharge tube 22.

[0156] As shown in FIG. 7(b), this embodiment performs control so thatluminous flux emitted from the vicinity of the central area of thedischarge tube 22 becomes parallel to the optical axis L, but in thecase where the light source is a point light source, it is possible toprovide a lighting optical system with an extremely narrow irradiationrange as shown in the figure. However, since the light-emitting sectionof the discharge tube 22 actually exists as a limited light-emittingarea equivalent to the inner diameter of the discharge tube 22, thisembodiment provides a light distribution characteristic such thatluminous flux spreads within a certain angle range centered on thevicinity of the irradiation optical axis rather than spreading within anextremely narrow irradiation angle range as shown in the figure.

[0157] An actual measurement shows a light quantity half the centrallight quantity and irradiation angle spreading about 15° with respect tothe sectional direction shown in the figure.

[0158]FIG. 10(a) and 10(b) show a lighting apparatus, which is anotherembodiment of the present invention. This embodiment is an example ofmodification to the first embodiment and FIG. 10(a) is a longitudinalsectional view of main members of the optical system of theabove-described lighting apparatus and FIG. 10(b) adds a traced lines oflight from the center of the light source to the sectional view of FIG.10(a).

[0159] Since the shape of the remaining area other than this section isalmost the same as the shape of the first embodiment, detailed drawingsthereof will be omitted.

[0160] This embodiment is obtained by deforming the shape of the threereflecting surfaces in the upper and lower sides of the optical memberof the first embodiment in order to reduce the size of the lightingapparatus in the vertical direction explained in the first embodiment.

[0161] In FIG. 10(a), the shape of the optical member 4 of the firstembodiment is indicated by two-dot dashed line and the shape of theoptical member 34 of this embodiment is indicated by solid line.

[0162] According to this embodiment, the size L₁ of the optical member34 in the vertical direction is smaller than the size L₀ of the opticalmember 4 in the vertical direction of the first embodiment byapproximately 20%. Furthermore, the irradiation angle and lightdistribution characteristic of the illuminating light are almost thesame as those of the first embodiment.

[0163] In FIG. 10, reference numeral 32 denotes a discharge tube,reference numeral 33 denotes a reflector and reference numeral 34denotes an optical member, and these are functionally almost equivalentto those of the first embodiment. However, the shape of the opticalmember 34 on the discharge tube 32 side and the shape of each reflectingsurface in particular are the features of this embodiment and thisembodiment intends miniaturization by optimizing these shapes.

[0164] In the same figure, the inner and outer diameters of the glasstube of the discharge tube 32 are indicated. As in the case of theabove-described two embodiments, luminous flux emitted from the centerof the discharge tube 32 is assumed to be representative luminous fluxfor simplicity of explanation and only luminous flux emitted from thecenter of the discharge tube 32 is shown in the figure. As an actuallight distribution characteristic, the light distribution characteristicchanges in the direction in which the light distribution as a wholeslightly spreads due to luminous flux emitted from the peripheralsections of the discharge tube 32 in addition to the representativeluminous flux shown in the figure, but the light distributioncharacteristic has almost the same tendency, and therefore thisembodiment will be explained according to this representative luminousflux below.

[0165] First, the shape of the lighting optical system of theabove-described lighting apparatus will be explained sequentially. Withrespect to the section of the reflector 33 shown in FIG. 10, the shapeof the back of reflector 33 in the direction of the irradiation opticalaxis L is assumed to be semi-cylindrical (hereinafter referred to as“semi-cylindrical section 33 a”) almost concentric with the dischargetube 32 for the same reason as for the above-described two embodimentsand the reflector 33 is further provided with curved surface sections 33b and 33 b′ covering the back of the reflecting surfaces 34 g and 34 g′of the outermost prism section P in the vertical direction of theoptical member 34, flat surface sections 33 c and 33 c′ connecting theabove-described two curved surfaces 33 b and 33 b′ and semi-cylindricalsection 33 a.

[0166] Next, the shape of the optical member 34 will be explained. Toreduce the size of the optical member 34 in the vertical direction andobtain a uniform light distribution characteristic for the requiredirradiation range such as that obtained from the first embodiment, thisembodiment optimizes the shape of each section as follows.

[0167] First, as shown in FIG. 10(a) and 10(b), the optical member 34also has three layers of reflecting surfaces 34 c, 34 e, 34 g, 34 c′, 34e′ and 34 g′ in the same way as the first embodiment, whereas a lightdistribution of luminous flux reflected by their respective reflectingsurfaces is different from that of the first embodiment.

[0168] That is, this embodiment provides an angle characteristic in sucha way that, of the luminous flux reflected by the respective reflectingsurfaces, the luminous flux component closest to the optical axis ischanged to a member almost parallel to the optical axis and the angle atwhich the luminous flux intersects the optical axis L increasesgradually as the light incident on the reflecting surface goes away fromthe optical axis L.

[0169] In other words, each reflecting surface is shaped in such a wayas to have a uniform irradiation distribution within the rangecorresponding to only half the area of one side from the optical axis.

[0170] Then, each reflecting surface is placed symmetrically withrespect to the optical axis to obtain a uniform light distributioncharacteristic as the required irradiation range as a whole. This shapewill be explained more specifically below.

[0171] Each section of the optical member 34 is shaped as will beexplained below. First, a cylindrical lens surface 34 a is formed in thecentral area through which the irradiation optical axis L passes andprism sections P including first refracting surfaces 34 b and 34 b′ andfirst reflecting surfaces 34 c and 34 c′ are formed in the upper andlower sides centered on the optical axis L symmetrically in the verticaldirection outside the cylindrical lens surface 34 a.

[0172] Outside these prism sections P, other prism sections P includingsecond refracting surfaces 34 d and 34 d′, and second reflecting surface34 e and 34 e′ are formed in the upper and lower sides centered on theoptical axis L symmetrically in the vertical direction.

[0173] Outside these prism sections P, still other prism sections Pincluding third refracting surfaces 34 f and 34 f′, and third reflectingsurface 34 g and 34 g′ are formed in the upper and lower sides centeredon the optical axis L symmetrically in the vertical direction.Furthermore, a prism array is formed on the exit surface 34 h.

[0174] An optical action of the optical member 34 configured as shownabove will be explained using a light traced drawing in FIG. 10B.

[0175] First, a luminous flux directed to the vicinity of theirradiation optical axis is changed to a luminous flux with a lightdistribution characteristic, which is uniform within the requiredirradiation range with respect to this section by the cylindrical lenssurface 34 a formed on the entrance surface of the optical member 34that gives positive refracting power, and then goes out of the exitsurface 34 h. Since this luminous flux is completely the same as that ofthe first embodiment, this luminous flux is omitted in FIG. 10(b).

[0176] Then, luminous flux components emitted from the center of thedischarge tube 32 upward and downward at relatively large angles arerefracted through the first refracting surfaces 34 b and 34 b′ made upof flat surfaces, entered into the prism sections P and then most ofluminous flux is totally reflected by the first reflecting surfaces 34 cand 34 c′ made up of predetermined curved surfaces and are changed fromluminous flux components parallel to the optical axis L in such a waythat the angle at which the luminous flux components intersects theoptical axis L increases gradually (resulting in a distribution of acertain angle on the upper side and lower side in the figure). Then, theluminous flux goes out of the exit surface 34 h. Combining theirradiation ranges of the upper and lower luminous flux components makesit possible to obtain a uniform light distribution characteristic as awhole.

[0177] Furthermore, luminous flux components emitted from the center ofthe discharge tube 32 upward and downward at larger angles are refractedthrough the second refracting surfaces 34 d and 34 d′ made up of flatsurfaces, entered into the prism sections P and then most of luminousflux is totally reflected by the second reflecting surfaces 34 e and 34e′ made up of predetermined curved surfaces and changed from luminousflux components parallel to the optical axis L to members directeddownward and upward in the figure, and therefore it is possible toobtain luminous flux within an irradiation range almost equivalent tothe light distribution by the above-described first reflecting surfaces34 c and 34 c′. Then, combining the luminous flux components in thesetwo areas makes it possible to obtain a uniform light distribution.

[0178] On the other hand, the luminous flux components emitted from thecenter of the discharge tube 32 upward and downward at the largest angleare refracted through the third refracting surfaces 34 f and 34 f′ madeup of flat surfaces, entered into the prism sections P and then most ofluminous flux is totally reflected by the third reflecting surfaces 34 gand 34 g′ made up of predetermined curved surfaces and changed fromluminous flux components parallel to the optical axis L to membersdirected downward and upward in the figure, therefore it is possible toobtain luminous flux within an irradiation range almost equivalent tothe light distribution by the above-described first reflecting surfaces34 c and 34 c′. Then, combining the luminous flux components in thesetwo areas makes it possible to obtain a uniform light distribution.

[0179] Thus, luminous flux emitted from the center of the discharge tube32 is divided into luminous flux components in a total of four areas byan optical action of the cylindrical surface 34 a and three pairs ofrefracting surfaces and reflecting surfaces and these four luminous fluxcomponents are overlapped with one another with a same lightdistribution with respect to the section shown in FIG. 10, making itpossible to construct a lighting optical system with a uniform lightdistribution as a whole.

[0180] Thus, segmentizing the reflecting surfaces of the optical member34 into smaller portions than the conventional arts makes it possible toreduce the thickness of the optical member 34 as in the case of thefirst and second embodiments. Furthermore, since the edge E, which is aboundary between the refracting surface and reflecting surface, isplaced away from the center of the discharge tube 32, it is possible toprevent the optical resin material from being affected by radiant heatfrom the light source and thereby reduce adverse influences on theoptical characteristic.

[0181] Furthermore, as an effect specific to this embodiment, it ispossible to reduce the width (height) of the opening in the verticaldirection and drastically reduce the size of the opening of this type oflighting optical system in the vertical direction by limiting the lightdistribution to be controlled by the respective reflecting surfaces ofthe optical member 34 to the upper half or lower half.

[0182]FIG. 11 and FIG. 12 show a configuration of a lighting apparatus,which is another embodiment of the present invention. This is an exampleof modification to the above-described second embodiment. FIG. 11 is aperspective view of main members of the optical system of the lightingapparatus and FIG. 12 is a rear view of the optical member alone. Sincethe light traced lines and light distribution characteristic, etc. arealmost the same as those in the second embodiment, detailed explanationsthereof will be omitted.

[0183] This embodiment is a three-dimensional modification of the shapeon the entrance surface side of the optical member of the lightingapparatus explained in the second embodiment and mainly intended toimprove the light distribution characteristic toward four corners on thesurface of an object.

[0184] In FIG. 11 and FIG. 12, reference numeral 42 denotes a dischargetube, 43 denotes a reflector and 44 denotes an optical member. Thefunctions of these members are almost equivalent to those of the secondembodiment, but this embodiment is especially characterized by the shapeof each surface of the optical member 44 on the discharge tube 42 side.

[0185] In the same figure, the shape of the back of the reflector 43 inthe direction of the irradiation optical axis is semi-cylindrical(hereinafter referred to as “semi-cylindrical section 43 a”) almostconcentric with the discharge tube 42 and the reflector 43 is furtherprovided with toric surfaces 43 b and 43 b′ covering the back of theoutermost reflecting surfaces 44 e and 44 e′ of the optical member 44 inthe vertical direction and flat surface sections 43 c and 43 c′connecting the above-described two toric surfaces and semi-cylindricalsection 43 a.

[0186] On the other hand, as in the case of the second embodiment, theoptical member 44 includes a lens surface 44 a having positiverefracting power in the direction perpendicular to the optical axis(vertical direction) in the central area on the entrance surface sideand two layers of prism section each having a refracting surface andreflecting surface in the peripheral sections on the entrance surfaceside are formed on both the upper and lower sides.

[0187] However, this embodiment is different from the second embodimentin that the central lens surface 44 a and reflecting surfaces 44 c, 44c′, 44 e and 44 e′ are constructed of three-dimensional curved surfaces.

[0188] More specifically, the toric lens surface 44 a is formed in thecentral area through which the irradiation optical axis L passes as arefracting surface and conical first refracting surfaces 44 b and 44 b′and toric-surfaced first reflecting surfaces 44 c and 44 c′ making upthe prism sections are formed symmetrically in the vertical directionoutside the toric lens surface 44 a.

[0189] Outside these surfaces, the prism sections made up of conicalsecond refracting surfaces 44 d and 44 d′, and toric-surfaced secondreflecting surfaces 44 e and 44 e′ are formed symmetrically in thevertical direction. On the exit surface, a prism array 44 h is formed.

[0190] A condensing operation and effects resulting from shaping theoptical member 44 in this way will be explained.

[0191] First, with respect to the refracting surface 44 a in the center,the section of the central area in the vertical direction is almostequivalent to that in FIG. 7(b) shown in the second embodiment, but theshape changes gradually toward the peripheral sections, the verticalwidth also changes and refracting power of each section also changesgradually.

[0192] This makes it possible to make the light distributioncharacteristic of the system as a whole uniform and prevent variationsin light distribution which is curved on the irradiated surface of anobject, which are likely to occur on the boundary edge between therefracting surface and reflecting surface of the prism sections P.

[0193] Furthermore, using a toric-surfaced configuration not only forthe above-described central area but also for the reflecting surface 44c, 44 c′, 44 e and 44 e′ in the peripheral sections, on which sectionalshapes in the horizontal and vertical directions change graduallyaccording to their respective positions makes it possible to providelight distribution characteristic uniform toward all four corners in theirradiation range.

[0194] Thus, with respect to luminous flux emitted from the center ofthe discharge tube 42, it is possible to construct a lighting opticalsystem with a narrow irradiation angle range and a highly condensedlight distribution as a whole through an action of each reflectingsurface made up of the toric surface 44 a and a pair of toric surfaces.

[0195] Furthermore, segmenting the reflecting surfaces of the opticalmember 44 into smaller portions than the conventional arts makes itpossible to reduce the thickness of the optical member 44 as in the caseof the above-described embodiments. Moreover, since the boundary edgebetween the refracting surface and reflecting surface goes away from thecenter of the light source, it is possible to prevent the optical resinmaterial from being affected by radiant heat from the light source andreduce adverse influences on the optical characteristic.

[0196] Furthermore, using a toric-surfaced configuration for therefracting surfaces in the central area and each reflecting surface,this embodiment has a specific effect of making it possible to easilyconstruct a lighting optical system with a uniform light distributioncharacteristic toward four corners in the irradiation range without anyadditional special optical system.

[0197] As described above, the above-described embodiments include aplurality of prism sections with refracting surfaces and reflectingsurfaces having total reflex action arranged in the directionquasi-perpendicular to the longitudinal direction of the light source,making it possible to drastically reduce the thickness of the opticalmember, and therefore reduce the thickness of the overall lightingapparatus. Moreover, use of a condensing action through reflectionsmakes it possible to efficiently use light from the light source andimplement a lighting apparatus, which is small in size yet withexcellent optical characteristics. Thus, this embodiment can provide alighting apparatus best suited to mounting on a small image pickupapparatus such as a card type camera in particular.

[0198] Especially, since light is controlled by refraction and totalreflection by the optical member, there is light quantity loss and it ispossible to control all light inside the prism and significantly reducethe size of the entire lighting apparatus.

[0199] Furthermore, determining the shape of reflecting surfaces of theoptical member appropriately makes it easier to obtain an almost uniformlight distribution on the irradiation area.

[0200] By the way, it is also possible to control a light distributionof a direct light component from the light source passing near theoptical axis and a light distribution of a reflected light componentforming a certain angle with respect to the optical axis separatelyusing a single optical member by forming a lens section having positiverefracting power in the central area in the directionquasi-perpendicular to the longitudinal direction of the light source onthe plane of incidence of the optical member and forming theabove-described plurality of prism sections in the peripheral section.

[0201] Then, by determining the shape of each surface of the pluralityof prism sections so that the irradiation range of light emitted fromthe optical member through these prism sections virtually matches(overlaps) the irradiation range of light emitted through the lenssection, it is possible to obtain an almost uniform light distributioncharacteristic on the irradiation area of illuminating light.

[0202]FIG. 13 to FIG. 17 show a lighting apparatus, which is anotherembodiment of the present invention, and especially this embodimentshows an apparatus that emits electronic flash incorporated in a camera.FIG. 13 is a sectional view of the optical system of the above-describedlighting apparatus cut with a plane including the radial direction ofthe discharge tube (the plane perpendicular to the longitudinaldirection of the discharge tube), FIG. 14 illustrates a comparisonbetween the case of the above-described lighting apparatus and the casewithout the features of the above-described lighting apparatus, FIG. 15is a sectional view of the optical system of the above-describedlighting apparatus cut with a plane including the center axis of thedischarge tube, FIG. 16 is an exploded perspective view of the opticalsystem of the above-described lighting apparatus and FIG. 17 is aperspective view viewed from the back of the optical member used for theabove-described lighting apparatus. FIG. 18 shows a camera equipped withthe above-described lighting apparatus.

[0203]FIG. 13 to FIG. 15 also show traced lines of representative lightbeams emitted from the center of the light source and especially FIG. 13and FIG. 14 show different luminous flux components emitted from thecenter of the light source on the same section according to thedifferent positions of incidence on the optical member.

[0204] First, FIG. 18(a) shows a so-called compact camera incorporatingthe lighting apparatus of this embodiment and FIG. 18(b) shows aso-called card size camera incorporating the lighting apparatus of thisembodiment.

[0205] In these figures, reference numeral 211 denotes the body of thecamera and 212 denotes a lens barrel of a picture-taking lens placed inalmost the center of the front side of the camera body 211. Referencenumeral 201 is the lighting apparatus of this embodiment placed at thetop right of the camera body 211.

[0206] Reference numeral 213 denotes a shutter release button, 217denotes an inspection window of a photometer to measure brightness ofexternal light and 218 denotes an inspection window of a finder.

[0207] Furthermore, reference numeral 214 denotes an operation member tozoom the picture-taking lens and depressing this operation memberfrontward allows an image to zoom in and depressing this operationmember backward allows an image to zoom out. Reference numeral 215denotes a mode setting button to switch between various modes of thecamera and 216 denotes a liquid crystal display window to inform theuser of the operation of the camera. The camera in which the lightingapparatus of the present invention is incorporated is not limited to thecamera shown in FIG. 18, but can also be incorporated in other cameras(single-lens reflex camera and video camera, etc.).

[0208] Then, the members that determine optical characteristics of thelighting apparatus of this embodiment will be explained in detail usingFIG. 13 to FIG. 17.

[0209] In these figures, reference numeral 102 denotes a cylindricallight-emitting discharge tube (xenon tube). Reference numeral 103denotes a reflector (reflection member, first reflector) that reflectsforward the luminous flux component directed backward andupward/downward in the direction of the irradiation optical axis L ofthe luminous flux emitted from the light-emitting discharge tube 102.This reflector has a high-reflectance inner surface made of a metallicmaterial such as radiant aluminum or a resin material having an innersurface on which a high-reflectance metal-evaporated surface is formed.

[0210] Reference numeral 104 is an optical member made up of a one-piecetransparent body. The central area through which the irradiation opticalaxis L passes on the entrance surface side of the optical member 104, acylindrical lens surface 104 a is formed which has positive refractingpower in the direction quasi-perpendicular to the longitudinal directionof this light-emitting discharge tube 102. In upper and lower peripheralsections 104 b and 104 b′, a parallel flat surface is formed.Furthermore, between the cylindrical lens surface 104 a and the upperand lower peripheral sections 104 b and 104 b′, is formed a pair ofprism sections (reflecting sections) P made up of refracting surfaces(entrance surface) 104 c and 104 c′ and reflecting surfaces 104 d and104 d′ respectively.

[0211] To make it easier to understand the shape of this optical member104, FIG. 17 shows a perspective view viewed from the back of theoptical member 104. As the material for the above-described opticalmember 104, high transmittance optical resin material such as acrylicresin or glass material is suitable.

[0212] When the camera operating mode of the camera and lightingapparatus in the above-described configuration is set, for example, to a“electronic flash auto mode”, after the user presses the shutter releasebutton 213, a central processing unit (not shown) decides whether or notallow the lighting apparatus 201 to emit light according to thebrightness of external light measure by the photometer (not shown) andsensitivity of a film loaded or the characteristic of an image pickupdevice such as a CCD or CMOS.

[0213] When the central processing unit decides that “the lightingapparatus should be instructed to emit light” in a situation of takingpictures, the central processing unit outputs a light-emitting signaland a light-emitting control circuit (not shown) instructs thelight-emitting discharge tube 2 to emit light through a trigger leadwire attached to the reflector 203.

[0214] Of the luminous flux emitted from the light-emitting dischargetube 202, the luminous flux emitted backward in the direction ofirradiation optical axis L and upward/downward is reflected by thereflector 203 and entered into the optical member 204 positioned infront side, while the luminous flux emitted forward in the direction ofirradiation optical axis L is directly entered into the optical member204, and this luminous flux is changed to luminous flux with apredetermined light distribution characteristic by the optical member204 and then irradiated onto an object.

[0215] Then, an optimal method of setting the optical system of thelighting apparatus according to this embodiment which is thin-shaped andcapable of irradiating illuminating light uniformly and efficientlywithin a required irradiation range will be explained using FIG. 13 toFIG. 15 below.

[0216]FIG. 13 and FIG. 14 show a longitudinal sectional view of thelighting apparatus according to this embodiment cut with the planeincluding the radial direction of the light-emitting discharge tube andshow a basic concept for optimizing the light distributioncharacteristic in the vertical direction. FIG. 13(a) and 13(b) and FIG.14(a) and 14(b) show light traced lines on the same section in differentcases and reference numerals in the figures correspond to those in FIG.15 to FIG. 17.

[0217] In the same figures, inner and outer diameters of the glass tubeof this light-emitting discharge tube 102 are indicated. As an actuallight-emitting phenomenon of the light-emitting discharge tube of thistype of the lighting apparatus, light is often emitted from the fullinner diameter to improve the efficiency and it is reasonable toconsider that light is emitted virtually uniformly from light-emittingpoints across the full inner diameter of the discharge tube. However,for simplicity of explanation, suppose the luminous flux emitted fromthe center of the discharge tube 102, that is the light source, is therepresentative luminous flux and the figures only show thisrepresentative luminous flux. As an actual light distributioncharacteristic, the light distribution characteristic as a whole changesin a direction in which luminous flux spreads slightly due to luminousflux emitted from the periphery of the light-emitting discharge tube 102in addition to the representative luminous flux as shown in the figures,but this luminous flux has almost an identical tendency of lightdistribution characteristic, and therefore the following explanationswill be based on this representative luminous flux.

[0218] The shape of the back of the reflector 103 facing the center ofthe light source in the direction of the irradiation optical axis L issemi-cylindrical (hereinafter referred to as “semi-cylindrical section103 a”) almost concentric with the light-emitting discharge tube 102.This is a shape, which is effective to return the light reflected by thereflector 103 to the vicinity of the center of the light source againand has the effect of preventing adverse influence from refractions ofthe glass part of the light-emitting discharge tube 102.

[0219] Furthermore, such a configuration makes it possible to handle thereflected light by the reflector 103 as the outgoing light almostequivalent to the direct light from the light source, and thereby reducethe overall size of the optical system that follows this.

[0220] Furthermore, the reason that the reflector 103 has asemi-cylindrical shape is that having a size smaller than this willrequire the size of the optical member 104 to be increased to condenseluminous flux in the vertical direction, while having a size larger thanthis will increase luminous flux trapped inside the reflector 103,resulting in deterioration of efficiency.

[0221] On the other hand, the upper and lower peripheral sections 103 band 103 b′ of the reflector 103 are formed in such a way as to cover thefront space between the light-emitting discharge tube 102 and opticalmember 104 and formed to have a curved surface so that the luminous fluxreflected by these peripheral sections has a certain uniform lightdistribution characteristic.

[0222] Then, the shape of the optical member 104 that gives the greatestinfluence on the light distribution characteristic of this lightingapparatus will be explained. This embodiment adopts the followingconfiguration, which is thinnest in the direction of the optical axis,to obtain a uniform light distribution within the required irradiationrange.

[0223] First, as shown in FIG. 13(a), in the central area on theentrance surface of the optical member 104 a cylindrical lens surface104 a having positive refracting power within the plane perpendicular tothe irradiation optical axis L is formed. In this way, the luminous fluxpassing near the irradiation optical axis L out of the luminous fluxemitted from the light-emitting discharge tube 102 is changed toluminous flux having a uniform light distribution within a predeterminedangle range and then goes out of the plane 104 e of the optical member104.

[0224] Here, to have a uniform light distribution characteristic, thecylindrical lens surface 104 a of the optical member 104 is constructedto have a continuous non-spherical shape so that a proportionalrelationship is established between the angle of outgoing light from thecenter of the discharge tube 102 and the angle of outgoing light thathas passed through the optical member 104, and luminous flux iscondensed at a certain rate.

[0225] Then, as described in FIG. 13(b), of the luminous flux emittedfrom the center of the discharge tube 102, the luminous flux componentswhich form a large angle with the optical axis and which directly enterinto the peripheral sections 103 b and 103 b′ of the reflector 103 willbe explained. Here, the peripheral sections 103 b and 103 b′ of thereflector 103 are shaped so that after reflection the above-describedmembers have almost the same irradiation angle range and uniformdistribution as those in FIG. 13(a).

[0226] The luminous flux reflected by the peripheral sections 103 b and103 b′ of the reflector 103 enters from the peripheral sections 104 band 104 b′ of the optical member 104 into the optical member 104 andgoes out of the exit surface 104 e. However, the peripheral sections 104b and 104 b′ of the optical member 104 have no power in the directionperpendicular to the irradiation optical axis L (vertical direction) andluminous flux passing through this area is irradiated with the samelight distribution characteristic adjusted by the peripheral sections103 b and 103 b′ of the reflector 103.

[0227] Thus, the peripheral sections 103 b and 103 b′ of the reflector103 have the function of uniformly condensing the luminous flux directlyentering from the discharge tube 102 within a certain angle range andleading the reflected luminous flux to the narrow passing areas of theperipheral sections 104 b and 104 b′ of the optical member 104 as well.As a result, it is possible to obtain a uniform light distribution withrespect to the required irradiation range as in the case of FIG. 13(a).Furthermore, the peripheral sections 103 b and 103 b′ of the reflector103 and cylindrical lens surface 104 a form light paths completelydifferent from each other to perform condensing (irradiation) control.

[0228] Then, the light path through the prism sections, which is themost characteristic configuration of this embodiment, will be explainedusing FIG. 14(a). To make the explanation easier to understand, anexample where no prism section is provided will be shown in FIG. 14(b).

[0229] First, as shown in FIG. 14(b), when the optical system of thissection is constructed of only the refraction area of the cylindricallens surface 104 a shown in FIG. 13(a) above and the reflection area ofthe reflector 103 shown in FIG. 13(b), passing luminous flux whoseirradiation is uncontrollable by these areas is produced unavoidablywithin the required irradiation range.

[0230] That is, this luminous flux is indicated by two-dot dashed linesA, A′ and B, B′ in FIG. 14(b) and realizing an efficient condensingaction in this configuration will require the sizes of the reflector 103and optical member 104 to be increased considerably.

[0231] An example of such a large sized optical system is an opticalsystem which has a semi-ellipsoidal reflector whose approximate focalpoint coincides with the center of the light source and in which theirradiation angle distribution of the light reflected by the reflectormatches the distribution of direct light limited by the aperture of thereflector.

[0232] In this case, however, such a system cannot be constructed unlessthe depth of the optical system in the direction of the optical axis isconsiderably large.

[0233] On the contrary, as shown in FIG. 14(a), when prism sections Pare provided between the cylindrical lens surface 104 a on the entrancesurface and the peripheral sections 104 b and 104 b′ of the opticalmember 104, the luminous flux incident on the refracting surface 104 cand 104 c′ made up of flat surfaces (luminous flux passing as indicatedby two-dot dashed lines A, A′ and B, B′ in FIG. 14(b) is refractedthrough the refracting surface 104 c and 104 c′, entered into the prismsections, almost totally reflected by the reflecting surfaces 104 d and104 d′made up of predetermined curved surfaces and changed to luminousflux having a light distribution characteristic almost equivalent to theirradiation angle distributions shown in FIG. 13(a) and 13(b) above.

[0234] Here, as shown in the figure, the angle range of the luminousflux incident on the refracting surfaces 104 c and 104 c′ isconsiderably narrow compared to the angle range of the luminous fluxshown in FIG. 13(a) and 13(b). For this reason, in order to fit theirradiation angle range of the luminous flux incident on the reflectingsurfaces 104 c and 104 c′ into the irradiation angle range shown in FIG.13(a) and 13(b), it is necessary to determine the shape of thereflecting surfaces 104 c and 104 c′ in such a way that the irradiationangle range of the reflected light spreads considerably at a certainrate.

[0235] Based on this concept, this embodiment optimizes the shapes ofthe reflecting surfaces 104 d and 104 d′ to non-spherical shapes so thatthe irradiation angle range of luminous flux incident on the refractingsurfaces 104 c and 104 c′ virtually matches (overlaps) the cylindricallens surface 104 a shown in FIG. 13(a) and 13(b) and the irradiationangle range of the reflector 103.

[0236] Thus, all luminous flux emitted from the center of the dischargetube 102 is changed to luminous flux having a uniform light distributionin the direction perpendicular to the longitudinal direction (verticaldirection) of the discharge tube 102 by respective optical actions ofthe cylindrical lens surface 104 a shown in FIG. 13(a), the peripheralsections 103 b and 103 b′ of the reflector 103 shown in FIG. 13(b) andthe prism sections (refracting surfaces 104 c and 104 c′ and reflectingsurface 104 d and 104 d′) P shown in FIG. 14(a), and these three typesand a total of five layers of irradiation angle ranges are overlapped,which provides an efficient way to obtain a uniform light distributioncharacteristic as a whole.

[0237] On the other hand, as described above, the luminous flux emittedbackward from the center of the discharge tube 102 is reflected by thesemi-cylindrical section 103 a of the reflector 103, passes through thecenter of the discharge tube 102 again and then goes out in theirradiation optical axis L. The behavior of the light beams thereafteris the same as that explained in FIG. 13(a), FIG. 13(b) and FIG. 14(a).

[0238] Here, an optimal distribution ratio between the cylindrical lenssurface 104 a of the optical member 104, reflector 103 and the prismsection P of the optical member 104 will be explained using FIG. 14(a).

[0239] In this embodiment, it is preferable that the area of thecylindrical lens surface 104 a shown in FIG. 13(a) and the reflectionarea by the reflector 103 shown in FIG. 13(b) form a basic condensingoptical system and the minimum area connecting these areas beconstructed of a reflection optical system (hereinafter referred to as“total reflection area”) using a total reflex action by the prismsections P whose light path is shown in FIG. 14(a).

[0240] For the total reflection area of these prism sections P, it ispreferable that an angle α formed by the straight line connecting thecenter of the discharge tube 102 and the ends of the total reflectionarea of the prism sections P with the irradiation optical axis L bewithin the following angle range:

20°≦α≦70°  (1)

[0241] Here, if the angle α is smaller than 20° which is the lower limitin Formula (1), totally reflection of most incident luminous flux by thereflecting surface 104 d and 104 d′ of the reflection optical systemitself becomes difficult. That is, if the angle α is smaller than 20°,the angle of the prism sections P become considerably acute, requiring ashape which is deep in the thickness direction. This will make itdifficult not only to construct but also to manufacture a thin-shapedoptical system, which is a main subject of this embodiment.

[0242] On the other hand, when the angle α is greater than 70° which isthe upper limit in formula (1), the condensing area by the reflector 103decreases and the fact that the reflection area has been divided intothe reflection area by the reflector 103 and the reflection area by theprism sections P itself becomes meaningless. That is, although it ispossible to divide the light path through the optical system proposedthis time and realize a uniform light distribution control within therequired irradiation angle range through independent control by thereflector 103, the light path in this area is not used effectively.Furthermore, when the angle α is greater than the upper limit 70°, theaperture of the optical system in the vertical direction increases, inwhich case the thickness can be reduced but the increase of the aperturein the vertical direction will result in an increase of the overall sizeof the optical system, which is not preferable.

[0243] As an ideal mode, it is preferable to narrow this totalreflection area to a necessary minimum and organize the system in such away as to reduce light quantity loss and such a configuration makes itpossible to minimize the thickness direction, make the shape simple andmake the system easy to process.

[0244] In view of the above-described situation, this embodiment setsthis total reflection area within a 20° range from 40° to 60° foroptimization.

[0245] Then, optimal shapes for the refracting surfaces 104 c and 104 c′which will lead luminous flux to the reflecting surfaces 104 d and 104d′ of the prism sections P shown in FIG. 14(b) will be explained.

[0246] As is apparent from FIG. 14(a), luminous flux emitted from thecenter of the discharge tube 102 is largely refracted through refractingsurfaces 104 c and 104 c′, led in the direction away from theirradiation optical axis L and reach the reflecting surfaces 104 d and104 d′. The ideal shapes of these refracting surfaces 104 c and 104 c′are the ones that will allow the largest possible part of luminous fluxemitted from the discharge tube 102 is led to the reflecting surfaces104 d and 104 d′ and for this purpose, it is effective to adopt aconfiguration that luminous flux is refracted abruptly through therefracting surfaces 104 c and 104 c′.

[0247] This will also lead to shortening of the reflecting surfaces 104d and 104 d′ and a reduction of the size of the optical system in thethickness direction.

[0248] As a specific shape, it is preferable that the gradient of therefracting surfaces 104 c and 104 c′, which are flat surfaces, withrespect to the irradiation optical axis L be 0°. However, it isdifficult to realize a flat surface with a gradient of 0° for reasonsrelated to the processing accuracy due to the problem of moldability ofthe optical member 104. Therefore, this embodiment constructs theserefracting surfaces 104 c and 104 c′ as flat surfaces whose gradient θwith respect to the optical axis L is 4° or less also taking intoaccount processing requirements. It is also possible to construct theserefracting surfaces 104 c and 104 c′ with curved surfaces, which areeasier to process.

[0249] On the other hand, this embodiment is expected to have theunprecedented characteristic effects specific to this embodiment bysegmenting the optical control area into smaller portions andoverlapping ranges of irradiation from different control areas with oneanother.

[0250] First, the reflecting surfaces are constructed of discretesurfaces made of materials of different types instead of surfacescontinuously arranged in the direction of the irradiation optical axisas in the case of conventional arts and those reflecting surfaces areplaced overlapping with one another in the direction quasi-perpendicularto the irradiation optical axis L.

[0251] Such a configuration makes it possible to significantly reducethe thickness of the lighting optical system in the depth direction,which is the most outstanding feature of this embodiment. That is, aswill be explained using FIG. 13(a), 13(b) and FIG. 14(a), reflectingsurfaces 104 d and 104 d′ are placed as the first reflection layers andthe peripheral sections 103 b and 103 b′ of the reflector 103, which arethe second reflection layers, are placed outside the reflecting surfaces104 d and 104 d′ at positions in the direction of the optical axis Loverlapping with them, thus making it possible to reduce the overalllength of the reflecting surfaces in the direction of the optical axisL.

[0252] Second, it is possible to significantly reduce the thickness ofthe optical member 104 itself. That is, the configuration essential tothe optical member 104 only includes the cylindrical lens surface 104 ahaving positive refracting power near the irradiation optical axis L andthe prism sections P to separate luminous flux directly incident fromthe discharge tube 102 and luminous flux reflected by the reflector 103,and it is possible to reduce the thickness of the peripheral sections104 b and 104 b′ which are the outermost areas. They are simple inshape, yet they can function sufficiently, which makes it possible tosignificantly reduce the overall thickness of the optical member 104.

[0253] This makes it possible not only to improve moldability of theoptical member 104 but also to minimize a reduction of light quantitywhen light passes through resin material. It further contributes to areduction of weight of the image pickup apparatus and other opticalequipment to be mounted with this lighting apparatus. Moreover, theshape of the outermost surface is extremely simple and is constructed ofsurfaces with fewer optical restrictions, and therefore it is easy tomaintain the optical member 104, and even when mounted on variousoptical apparatuses, there is no need to adopt any special supportstructure, providing a configuration quite easy to handle.

[0254] Third, adopting a plurality of reflection layers can preventproblems with a conventional light guide type electronic flash, that is,the problem that when an optical member made of a resin optical materialis placed near the light source, heat produced from the light sourcedeforms the optical member, making it impossible to obtain the originaloptical characteristic depending on the light-emitting condition. Thatis, providing a plurality of layers of reflecting surfaces in this waymakes it possible to place the edge E, which is a boundary between therefracting surface and reflecting surface of the optical member, whichis most vulnerable to heat, away from the light source and also expandthe space around the light-emitting discharge tube 102, and therefore itis possible to minimize influences on resin materials (optical member104) of radiant heat and convection heat produced during continuouslight emissions and prevent deterioration of the optical characteristic.

[0255] Thus, this embodiment can construct a small, thin shape andextremely efficient lighting optical system with little light quantityloss due to irradiation to the outside of the required irradiation rangeusing a fewer members such as the reflector 103 and optical member 104.

[0256] Next, a condensing action of this embodiment in the longitudinaldirection of the discharge tube will be explained using FIG. 15.

[0257]FIG. 15 shows a sectional view when the optical system is cut witha plane including the center axis of the light-emitting discharge tube102 and also shows a traced lines of light from the center in thelongitudinal direction and from the center in the radial direction ofthe discharge tube 102 together.

[0258] As shown in the figure, the side of the optical member 104 fromwhich luminous flux goes out is constructed of a prism section 104 fformed in the central area in the longitudinal direction of thedischarge tube 102 with both slopes having the same angle and Fresnellens sections 104 g and 104 g′ formed in the peripheral sections. Inthis embodiment, apex angle of the prism section 104 f in the centralarea is fixed to 105°.

[0259] The prism section 104 f in the central area of the optical member104 formed in such the angle setting has the effect of allowing aluminous flux component with a relatively large angle of incidence(member whose angle in the prism section after incidence is 30° to 40°)to go out of the plane with the same angle of refraction on the entrancesurface, that is, the effect of allowing this luminous flux to go out ofthe exit surface with little influence of refraction on the exit surfaceas well as the effect of condensing the incident luminous flux toluminous flux within a certain irradiation angle range.

[0260] This embodiment has described the case where the apex angle ofthis prism section 104 f is fixed to 105°, but this embodiment is notlimited to this angle and setting it to a smaller angle, for example,90° makes it possible to narrow the irradiation angle range after theluminous flux goes out of the optical member 104. On the other hand,widening the apex angle, for example, to 120° makes it possible to widenthe irradiation angle range after luminous flux goes out of the opticalmember 104.

[0261] On the other hand, as also shown in FIG. 15, part of luminousflux incident on the prism section 104 f is almost totally reflected bythe prism surface and is returned to the discharge tube 102 side again.This luminous flux is reflected by the reflector 103, entered into theoptical member 104 again, changed to a predetermined angle component bythe prism section 104 f or Fresnel lens sections 104 g and 104 g′ andthen irradiated onto an object.

[0262] Thus, most of luminous flux emitted from the center of thedischarge tube 102 is changed to luminous flux with a certain angledistribution and goes out of the optical member 104. The lightdistribution of illuminating light in this case is only dependent on theangle setting of the apex angle of the prism section 104 f and notaffected by the pitch, etc. of the prism section 104 f. Thus, it ispossible to perform condensing control in an extremely shallow areawithout the need for the depth in the direction of the optical axis L,and thereby drastically reduce the size of the overall optical system.

[0263] Furthermore, as shown in the figure, Fresnel lens sections 104 gand 104 g′ are formed in the peripheral sections on the exit surfaceside of the optical member 104. Though the optical member 104 isconstructed in a thin shape, the area peripheral to the optical member104 is an area where luminous flux has certain directivity and forming aFresnel lens section in this part makes it possible to performcondensing action relatively efficiently.

[0264]FIG. 15 shows no outstanding condensing action, but this isbecause only luminous flux emitted from the center of the discharge tube102 is shown and with respect to the luminous flux emitted from theperiphery of the terminals at both ends of the discharge tube 102,considerable part of luminous flux is changed to a member concentratingnear the irradiation optical axis L.

[0265] Thus, adjusting the shape of the exit surface of the opticalmember 104 allows even quite a thin-shaped optical system close to thedischarge tube 102 to efficiently condense irradiation luminous fluxwithin a certain angle range.

[0266] Moreover, the light distribution in the longitudinal direction(horizontal direction) of the discharge tube 102 is controlled by acondensing action of the prism section 104 f on the outgoing light sideof the optical member 104 and Fresnel lens sections 104 g and 104 g′ andthe light distribution in the direction perpendicular to thelongitudinal direction (vertical direction) of the discharge tube 102 iscontrolled by an efficient condensing action of the cylindrical lenssurface 104 a on the entrance surface side of the optical member 104,prism section P and reflector 103. This provides an unprecedentedlythin-shaped lighting optical system with an excellent opticalcharacteristic.

[0267] This embodiment has described the case where the lightdistribution in the direction perpendicular to the longitudinaldirection of the discharge tube 102 is controlled by dividing lightdistribution into areas of three types and five layers by thecylindrical lens surface 104 a provided on the entrance surface side ofthe optical member 104, prism section P and reflector 103 so that theirradiation angle ranges of the respective areas overlap (match) withone other. However, the present invention is not limited to this mode.

[0268] That is, when the light source has a size exceeding a certainvalue, there may also be cases where it is preferable to differentiatethe irradiation angle ranges. For example, the irradiation angle of thecylindrical lens surface close to the light source has a tendency tospread considerably when the light source is large. On the other hand,the degree of condensing of a luminous flux component under the controlof the reflector farthest from the light source is not reduced even ifthe light source is relatively large, and the luminous flux componenthas a distribution not much deviated from the initially set irradiationangle distribution.

[0269] From this, it is preferable to set the cylindrical lens surfaceplaced close to the light source so that the irradiation angle range ofluminous flux emitted from the center of the light source is narrowerthan a preset desired irradiation angle range. Likewise, with respect tothe reflector and prism section, it is preferable to set the irradiationangle ranges one by one after reflections according to the positionsfrom the center of the light source instead of setting a commonirradiation angle range uniformly.

[0270] That is, it is preferable to preset an area near the light sourceso that the angle range of outgoing luminous flux from the center of thelight source becomes narrower and set the prism section away from thelight source so that the light distribution characteristic from thecenter of the light source becomes a desired light distributioncharacteristic, when the lighting optical system similar to thisembodiment is applied to a light source having a finite size which isnot negligible.

[0271] Furthermore, instead of overlapping all irradiation angle rangeswith one another, it is also possible to determine an irradiation anglerange for each area so that when combined, a uniform distribution isobtained as a whole.

[0272] Furthermore, this embodiment has described the case where theconfiguration of each entrance surface of the optical member 104 and theconfiguration of each exit surface are symmetrical with respect to theoptical axis L. However, this embodiment is not limited to such asymmetric shape.

[0273] For example, the prism sections P on the entrance surface side ofthe optical member 104 are placed symmetrically with respect to theoptical axis L, but the prism sections P need not be placed in suchsymmetric positions and can be placed asymmetrically. This is true notonly for the prism sections P but also for the shape of the reflector103 and the shape of the cylindrical lens surface 104 a in the centralarea.

[0274] Furthermore, with respect to the prism section 104 f formed inthe center in the longitudinal direction of the discharge tube 102 onthe exit surface side, it is also possible to use prisms with differentangle settings for the right and left sides so as to provide variationsin the light distribution characteristic between the rightward andleftward directions. Or with respect to the Fresnel lens sections 104 gand 104 g′ it is also possible to provide variations in the degree ofcondensing and variations in the overall light distributioncharacteristic.

[0275] Furthermore, this embodiment has described the case where theshapes of the peripheral sections 103 b and 103 b′ of the reflector 103are non-spherical so that luminous flux emitted from the center of thelight source have a uniform distribution on the irradiation surface, butthe shape of the reflector 103 is not limited to such a shape. Forexample, the shape can also be semi-ellipsoidal whose focal positioncoincides with the center of the light source.

[0276] Thus, by constructing the peripheral sections of the reflector103 with the semi-ellipsoidal surface and placing another focal positionof the semi-ellipsoidal surface near the exit surface of the opticalmember 104, it is possible to allow luminous flux controlled by thereflector 103 to converge within a narrow range and reduce the apertureof the lighting optical system in the vertical direction to a minimumsize.

[0277] Furthermore, this embodiment has described the case where theshape of the cylindrical lens surface 104 a formed in the central areaof the optical member 104 is non-spherical, but the cylindrical lenssurface 104 a is not always limited to the non-spherical shape and canalso be cylindrical. The cylindrical lens surface 104 a can also betoric lens surface taking into account the condensing performance of thedischarge tube 102 in the longitudinal direction.

[0278]FIG. 19 and FIG. 20 show a lighting apparatus, which is anotherembodiment of the present invention and especially this embodiment showsan apparatus incorporated in the camera that emits electronic flashlight. FIG. 19 and FIG. 20 are longitudinal sectional views of theoptical system of the above-described lighting apparatus cut with aplane including the radial direction of the discharge tube and also showtraced drawings of representative light emitted from the center of thelight source. Furthermore, FIG. 19 and FIG. 20 show luminous fluxemitted from the center of the light source on the same sectionaccording to the position of light incident on the optical member.

[0279] In the same figure, reference numeral 122 denotes alight-emitting discharge tube (xenon tube) and 123 denotes a reflector.The reflector 123 has almost the same shape as the reflector 103 in theabove-described embodiment (described in FIG. 13 to FIG. 18) and theback of the reflector 123 facing the center of the light source in thedirection of irradiation optical axis L is formed semi-cylindrical(hereinafter referred to as “semi-cylindrical section 123 a”) almostconcentric with the light-emitting discharge tube 122. Furthermore, theperipheral sections 123 b and 123 b′ of the reflector 123 are formed soas to cover the front space between the light-emitting discharge tube122 and optical member 124 and the peripheral sections 123 b and 123 b′are constructed of quasi-ellipsoidal curved surfaces of second order sothat the luminous flux reflected by the peripheral sections concentrateson the upper and lower peripheral sections 123 b and 123 b′ of theoptical member 124.

[0280] However, as is apparent from the illustrated shape, the ratio ofthe semi-cylindrical section 123 a to the peripheral sections 123 b and123 b′ is different from the above-described embodiment. That is, thesemi-cylindrical section 123 a of the reflector 123 is not just half thesize of a cylinder but is shaped so as to cover an area (area ofapproximately 160° in the shown configuration) slightly narrower thanthe semi-cylinder and the peripheral sections 123 b and 123 b′ aredeformed to make up for this lack of coverage.

[0281] The reason that the semi-cylindrical section 123 a is small isthat luminous flux reflected by this semi-cylindrical section 123 a isbasically a member that reenters the glass tube of the light-emittingdischarge tube 122 and this shape of the semi-cylindrical section 123 ais intended to prevent adverse influences produced in this case.

[0282] The adverse influences here refer to that luminous flux reentersor goes out of the discharge tube 122 through a glass tube and a lossmember is produced in this case which is caused by surface reflections,about four times on average in a direction which is different from theoriginally intended direction, reducing the amount of luminous fluxwhich can be utilized effectively. In order to minimize this lossmember, this embodiment extends the peripheral sections 123 b and 123b′, directly increases the member led by the optical member 124 of thelight reflected by the reflector 123 without the intermediary of thedischarge tube 122 and thereby excludes stray light caused by surfacereflection as much as possible and provides a highly efficient opticalsystem.

[0283] Reference numeral 124 is an optical member made up of a one-piecetransparent body. In the central area though which the irradiationoptical axis L passes on the entrance surface side of this opticalmember 124, a cylindrical lens surface 124 a having positive refractingpower in the direction perpendicular to the longitudinal direction ofthe light-emitting discharge tube 122 is formed and parallel flatsurfaces are formed in the upper and lower peripheral sections 124 b and124 b′, and furthermore two pairs of prism sections (reflectingsections) P having refracting surfaces 124 c and 124 c′, and reflectingsurfaces 124 d and 124 d′ are formed between the cylindrical lenssurface 124 a and the upper and lower peripheral sections 124 b and 124b′.

[0284] The most characteristic configuration of this embodiment is thattwo pairs of prism sections P are formed in the optical member 124.

[0285] As described above, even if the reflecting surfaces (peripheralsections 124 b, 124 b′) formed on the front side of is extended, this isa configuration without increasing the thickness of the lighting opticalsystem in the direction of the optical axis L, that is, theconfiguration effective to keep the thickness of the lighting opticalsystem almost the same as the lighting optical system explained in theabove-described embodiment. That is, if the irradiation range that canbe controlled by the above-described front reflecting surfaces is simplywidened in this condition, the aperture in the vertical direction of thereflector 123 is widened and at the same time the thickness in thedirection of the optical axis L is also increased. To avoid thissituation, the angle range of luminous flux controlled by the prismsection of the optical member 124 is widened to absorb this. As theconfiguration that widens the range of control by the prism section andavoids an increase of the thickness in the direction of the optical axisL, this embodiment adopts a method of forming a plurality of layers ofprism sections in the optical member 124.

[0286] The detailed shape of the optical system will be explained usinglight beam traced drawings shown in FIG. 19 and FIG. 20.

[0287] In the same figure, the inner and outer diameters of the glasstube are shown as the discharge tube 122. As in the case of theabove-described embodiment, for simplicity of explanation, luminous fluxemitted from the center of the light source is regarded asrepresentative luminous flux and these figures only show thisrepresentative luminous flux. The actual light distributioncharacteristic as a whole slightly changes in the direction in whichlight distribution characteristic spreads as a whole due to luminousflux emitted from the peripheral sections of the light-emittingdischarge tube in addition to the representative luminous flux shown inthe figure, but since the tendency of the light distributioncharacteristic is almost the same, this case will be explained accordingto this representative luminous flux below.

[0288] As shown in FIG. 19(a), in the central area on the entrancesurface side of the optical member 124, a cylindrical lens surface 124 ahaving positive refracting power within the plane perpendicular to theirradiation optical axis L is formed. In this way, luminous flux passingnear the irradiation optical axis L out of the luminous flux emittedfrom the discharge tube 122 is changed to luminous flux having a uniformlight distribution within a predetermined angle range and goes out ofthe exit surface 124 g of the optical member 124.

[0289] Here, in order to provide a uniform light distributioncharacteristic, the cylindrical lens surface 124 a of the optical member124 is constructed to have a continuous non-spherical shape so that aproportionality relation is established between the angle of outgoinglight from the center of the discharge tube 122 and the angle ofoutgoing light after luminous flux passes through the optical member 124and so that luminous flux is condensed at a certain rate.

[0290] Next, as shown in FIG. 19(b), a luminous flux component emittedfrom the center of the discharge tube 122, which forms a large anglewith the optical axis and which directly enters the peripheral sections123 b and 123 b′ of the reflector 123 will be explained. Here, theperipheral sections 123 b and 123 b′ of the reflector 123 are shaped soas to have almost the same irradiation angle range as that in FIG. 19(a)and uniform distribution after the above-described member is reflected.

[0291] The luminous flux reflected by the peripheral sections 123 b and123 b′ of the reflector 123 enters from the peripheral sections 124 band 124 b′ of the optical member 124 to the optical member 124 and goesout of the exit surface 124 g. However, the peripheral sections 124 band 124 b′ of the optical member 124 have no power in the directionperpendicular to the irradiation optical axis L (vertical direction) andthe luminous flux passing through this section is irradiated with thesame light distribution characteristic adjusted by the peripheralsections 123 b and 123 b′ of the reflector 123.

[0292] Thus, the peripheral sections 123 b and 123 b′ of the reflector123 have the functions of not only uniformly condensing luminous fluxwhich directly enters from the discharge tube 122 within a certain anglerange but also leading the reflected luminous flux to a narrow passingarea of the peripheral sections 124 b and 124 b′ of the optical member124, that is, the function of changing the direction. As a result, it ispossible to obtain a uniform light distribution for the requiredirradiation range as in the case of FIG. 19(a). Furthermore, theperipheral sections 123 b and 123 b′ of the reflector 123 and thecylindrical lens surface 124 a can perform condensing (irradiation)control forming completely different light paths independent of eachother.

[0293] Then, light paths through the prism sections, which is the majorcharacteristic of this embodiment shown in FIG. 20(a) and 20(b) will beexplained.

[0294] As shown in FIG. 20(a), of the upper and lower prism sectionsprovided between the cylindrical lens surface 124 a on the entrancesurface of the optical member 124 and the peripheral sections 124 b and124 b′, luminous flux incident on the refracting surfaces 124 c and 124c′ made up of flat surfaces of the prism sections P, which are insidewith respect to the optical axis is refracted through the refractingsurfaces 124 c and 124 c′, enters into the prism sections, almosttotally reflected by the reflecting surfaces 124 d and 124 d′ made up ofpredetermined curved surfaces and changed to luminous flux having alight distribution characteristic almost equivalent to the irradiationangle distribution in above-described FIG. 19(a) and 19(b).

[0295] Here, as shown in the figure, the angle range of luminous fluxincident on the refracting surfaces 124 c and 124 c′ is considerablynarrower than the angle range of luminous flux shown in FIG. 19(a) and19(b). Thus, in order to fit the irradiation angle range of luminousflux incident on the refracting surfaces 124 c and 124 c′ into theirradiation angle range shown in FIG. 19(a) and 19(b), it is necessaryto adjust the shapes of the reflecting surfaces 124 d and 124 d′ so thatthe irradiation angle range of the reflection luminous flux issignificantly spread at a certain rate.

[0296] Based on this concept, this embodiment uses optimizednon-spherical shapes as the shapes of the reflecting surfaces 124 d and124 d′ so that the irradiation angle range of luminous flux incident onthe refracting surfaces 124 c and 124 c′ almost matches (overlaps) theirradiation angle range of the cylindrical lens surface 124 a andreflector 123 shown in the FIG. 19(a) and 19(b).

[0297] Furthermore, as shown in FIG. 20(b), of the upper and lower prismsections P, luminous flux incident on the refracting surfaces 124 e and124 e′ made up of flat surfaces of the outer prism sections P isrefracted through the refracting surfaces 124 e and 124 e′, enters intothe prism sections P, almost totally reflected by reflecting surfaces124 f and 124 f′ made up of predetermined curved surfaces and changed toluminous flux having a light distribution characteristic almostequivalent to the irradiation angle distribution in above-described FIG.19(a) and 19(b).

[0298] Thus, all luminous flux emitted from the center of the dischargetube 122 is changed to luminous flux with a uniform light distributionon the section quasi-perpendicular to the longitudinal direction of thedischarge tube 122 by optical actions of the cylindrical lens surface124 a shown in FIG. 19(a), the peripheral sections 123 b and 123 b′ ofthe reflector 123 shown in FIG. 19(b), and the upper and lower prismsections (refracting surfaces 124 c and 124 c′, 124 e, 124 e′ andreflecting surfaces 124 d and 124 d′, 124 f, 124 f′) P shown in FIGS.20(a) and 20(b), and by overlapping irradiation angle ranges of thesefour types and a total of 7 layers with one another, it is possible toefficiently obtain a uniform light distribution characteristic as awhole.

[0299] On the other hand, as described above, luminous flux emitted fromthe center of the discharge tube 122 backward is reflected by thesemi-cylindrical section 123 a of the reflector 123, passes through thecenter of the discharge tube 122 again and then goes out forward in thedirection of the irradiation optical axis L. The behavior of theluminous flux thereafter is the same as that shown in FIG. 19 and FIG.20.

[0300] The shape of the discharge tube 122 in the longitudinal directionaccording to this embodiment is the same as that of the above-describedembodiment.

[0301] According to this embodiment described above, as in the case ofthe lighting apparatus of the above-described embodiment, it is possibleto construct a small, thin-shaped and extremely highly efficientlighting optical system with low light quantity loss due to irradiationto the outside the required irradiation range using only a small numberof members such as the reflector 123 and optical member 124.

[0302] Moreover, this embodiment allows the peripheral sections 123 band 123 b′ of the reflector 123 to wrap around the discharge tube 122 tothe back of the discharge tube 122 and forms two layers of prismsections P of the optical member 124 on both the upper and lower sides,and can thereby construct a lighting optical system utilizinglight-emitting energy from the discharge tube 122 more effectivelywithout increasing the overall size of the lighting optical systemcompared to the above-described embodiment.

[0303]FIG. 21 to FIG. 23 show a lighting apparatus, which is anotherembodiment of the present invention, especially an apparatusincorporated in a camera in this embodiment that emits electronic flashlight. FIG. 21 and FIG. 22 show longitudinal sectional views of theoptical system of the above-described lighting apparatus cut with aplane including the radial direction of the discharge tube and FIG.21(a) and 21(b) and FIG. 22(a) also show traced lines of representativelight emitted from the center of the light source. FIG. 21(a) and 21(b)and FIG. 21(a) also show different luminous flux components emitted fromthe center of the light source on the same section according to thepositions of luminous flux components incident on the optical member.FIG. 23 is an exploded perspective view of the optical system of theabove-described lighting apparatus.

[0304] In these figures, reference numeral 132 denotes a light-emittingdischarge tube (xenon tube) and 133 denotes a reflector (firstreflection member). This reflector 133 has almost the same shape as thereflector of the above-described embodiment (described in FIG. 19 andFIG. 20).

[0305] Furthermore, reference numeral 134 denotes an optical member madeup of a one-piece transparent body. In the central area through whichthe irradiation optical axis L passes on the entrance surface side ofthis optical member 134, a cylindrical lens surface 134 a havingpositive refracting power in the direction perpendicular to thelongitudinal direction (vertical direction) of the discharge tube 132 isformed, and parallel flat surfaces are formed in the upper and lowerperipheral sections 134 b and 134 b′. A high transmittance optical resinmaterial such as acrylic resin or glass material is suitable as thematerial of this optical member 134.

[0306] Furthermore, reference numerals 135 and 135′ denote reflectors(second reflection members) placed in an area between the cylindricallens surface 134 a. And the peripheral sections 134 b and 134 b′ of theoptical member 134 and their sections perpendicular to the longitudinaldirection of the discharge tube 132 are constructed of curved surfaces.Furthermore, at least the inner sides of these reflectors 135 and 135′are made of a high reflectance material and these reflectors 135 and135′ are much thinner than the reflector 133.

[0307] Then, an optimal method of setting the optical system of thelighting apparatus in this embodiment which is of a thin-shaped, capableof uniformly and efficiently irradiating illuminating light within therequired irradiation range, simplifying the shape of the optical member134 as much as possible to make it easier to process will be explainedusing FIG. 21 and FIG. 22.

[0308]FIG. 21 and FIG. 22 are sectional views of the lighting apparatusof this embodiment cut in the radial direction of the discharge tube andshow a basic concept for narrowing the light distribution characteristicin the vertical direction within a narrow irradiation angle. FIG. 21(a),21(b) and FIG. 22(a) show traced light beams on the same section indifferent cases and reference numerals in the figures correspond to themembers in FIG. 23.

[0309] In these figures, the inner and outer diameters of the glass tubeare shown as the discharge tube 132. As in the case of theabove-described embodiment, for simplicity of explanation, luminous fluxemitted from the center of the light source, that is, the discharge tube132 is regarded as the representative luminous flux and thisrepresentative luminous flux will be used in the following explanations.

[0310] The back of the reflector 133 facing the center of the dischargetube 132 in the direction of the irradiation optical axis L issemi-cylindrical (hereinafter referred to as “semi-cylindrical section133 a”) almost concentric with the discharge tube 132. This is a shapeeffective for returning light reflected by the reflector 133 to thevicinity of the center of the light source again and has the effect ofreducing adverse influences of refraction by the glass section of thelight-emitting discharge tube 132.

[0311] On the other hand, the upper and lower peripheral sections 133 band 133 b′ of the reflector 133 have curved surfaces so that thereflected luminous flux has a certain uniform light distributioncharacteristic.

[0312] Furthermore, as will be explained below, by determining theshapes of the optical member 134 and reflector 135, it is possible toobtain a light distribution, which is thin in the direction of theoptical axis L and uniform within the required irradiation range.

[0313] First, as shown in FIG. 21(a), luminous flux emitted from thedischarge tube 132 toward the vicinity of the irradiation optical axis Lis changed to luminous flux having a uniform light distribution within apredetermined angle range by the cylindrical lens surface 134 a and thengoes out of the exit surface 134 c of the optical member 134.

[0314] Here, to provide a uniform light distribution characteristic, thecylindrical lens surface 134 a of the optical member 134 is designed tohave a continuous non-spherical shape so that the angle of luminous fluxemitted from the center of the discharge tube 132 and the angle ofluminous flux going out after passing through the optical member 134have a proportional relation to condense the outgoing luminous flux at acertain rate.

[0315] Then, as shown in FIG. 21(b), of the luminous flux emitted fromthe center of the discharge tube 132, the luminous flux componentforming a large angle with the optical axis L and directly entering theperipheral sections 133 b and 133 b′ of the reflector 133 will beexplained. The peripheral sections 133 b and 133 b′ of the reflector 133are shaped so that the above-described member is reflected by theperipheral sections 133 b and 133 b′ and then spreads uniformly withinalmost the same irradiation angle range as that in FIG. 21(a).

[0316] The luminous flux reflected by the peripheral sections 133 b and133 b′ of the reflector 133 enters into the optical member 134 from theperipheral sections 134 b and 134 b′ of the optical member 134 and goesout of the exit surface 134 c. However, the peripheral sections 134 band 134 b′ of the optical member 134 have no power in the directionperpendicular to the longitudinal direction (vertical direction) of thedischarge tube 132 and luminous flux passing through these areas isirradiated with the same light distribution characteristic adjusted bythe peripheral sections 133 b and 133 b′ of the reflector 133.

[0317] Thus, the peripheral sections 133 b and 133 b′ of the reflector133 have the function of condensing the direct light from the dischargetube 132 within a certain angle range uniformly and the function ofchanging the direction, that is, leading the reflected luminous flux tothe narrow passing area of the peripheral sections 134 b and 134 b′ ofthe optical member 134. As a result, it is possible to obtain a uniformlight distribution within the required irradiation range as in the caseof FIG. 21(a). Furthermore, the peripheral sections 134 b and 134 b′ ofthe reflector 134 and the cylindrical lens surface 134 a can performcondensing (irradiation) control forming completely different lightpaths which are independent of each other.

[0318] Then, light paths through the reflector 135, which is the majorcharacteristic of this embodiment will be explained using FIG. 22(a).

[0319] As shown in the figure, reflectors 135 and 135′ control luminousflux passing through the boundary between the above-described two lightpaths. These reflectors 135 and 135′ are placed inside the reflector 133and positioned and kept by a support (not shown) so that the aperture isformed at a certain distance from the cylindrical lens section 134 a ofthe optical member 134 toward the periphery.

[0320] Moreover, as shown in the figure, the reflectors 135 and 135′ aremade up of curved surfaces which are concave toward the irradiationoptical axis L with respect to this section and luminous flux emittedfrom the center of the discharge tube 132 entering these reflector 135and 135′ follows the light path of being changed to have a certain angledistribution, entering the peripheral sections 134 b and 134 b′ of theoptical member 134 and going out of the exit surface 134 c. As a result,the luminous flux is changed to luminous flux having the lightdistribution characteristic almost equivalent to the irradiation angledistribution in FIG. 21(a) and 21(b).

[0321] Here, as shown in the figure, the irradiation angle range ofluminous flux incident on the reflectors 135 and 135′ is much narrowerthan the irradiation angle range of the luminous flux shown in FIG.21(a) and 21(a), but by optimizing the shapes of the reflectors 135 and135′ to widen the angle range at a certain rate, it is possible toalmost match the irradiation angle range with the irradiation anglerange of the cylindrical lens surface 123 a and reflector 133 shown inFIG. 21(a) and 21(b).

[0322] Thus, all luminous flux emitted from the center of the dischargetube 132 is changed to luminous flux having a uniform light distributionby optical actions of the cylindrical lens surface 134 a shown in FIG.21(a), the peripheral sections 133 b and 133 b′ of the reflector 133shown in FIG. 21(b) and reflectors 135 and 135′ shown in FIG. 22(a) inthe direction perpendicular to the longitudinal direction (verticaldirection) of the discharge tube 132 and overlapping irradiation angleranges of these three types and a total of five layers with one anothermakes it possible to efficiently obtain uniform light distributioncharacteristic as a whole.

[0323] On the other hand, luminous flux emitted from the center of thedischarge tube 132 backward is reflected by the semi-cylindrical section133 a of the reflector 133, passed through the center of the dischargetube 132 again and emitted forward in the direction of irradiationoptical axis L. The behavior of light beams from then on is the same asthat in FIG. 21(a), 21(b) and FIG. 22(a).

[0324] Here, an optimal area distribution ratio between the cylindricallens surface 134 a of the optical member 134, the reflector 133 and thereflectors 135 and 135′ will be explained using FIG. 22(b).

[0325] In this embodiment, it is preferable that the area of thecylindrical lens surface 134 a shown in FIG. 21(a) and the reflectionarea of the reflector 133 shown in FIG. 21(b) form a basic condensingoptical system and that the minimum area bridging between these areas beconstructed of the reflecting/condensing optical system using areflection action by the reflectors 135 and 135′ whose light path isshown in FIG. 22(a).

[0326] For the reflecting/condensing areas of these reflectors 135 and135′, it is preferable that an angle β between a straight lineconnecting the center of the discharge tube 132 and each end of thereflecting/condensing area of the reflectors 135 and 135′ and theirradiation optical axis L be within the following angle range:

35°≦β≦70°  (2)

[0327] Here, when the angle β is smaller than the lower limit 35° ofFormula (2), a distance H between points A and B increases where thepoint at which the straight line connecting the center of the dischargetube 132 and the end point A of the cylindrical lens surface 134 aintersects with the plane of incidence of the peripheral sections 134 band 134 b′ of the optical member 134 is B, which makes it impossible tosufficiently reduce the thickness of the lighting optical system, whichis the object of this embodiment. On the other hand, when the angle β isgreater than the upper limit 70°, the condensing area of the reflector133 decreases, rendering meaningless the fact that the system has beendivided into the reflector 133 and reflectors 135 and 135′.

[0328] An ideal mode is to reduce the condensing areas of thesereflectors 135 and 135′ to a necessary minimum and organize those areasinto a mode with little light quantity loss. Such a configuration makesit possible to reduce the length in the thickness direction to aminimum, simplify the shape and therefore make the system easy toprocess.

[0329] In view of such a situation, this embodiment sets thisreflecting/condensing area within an approximately 18° range from 42° to60° for optimization. This range is narrower than the total reflectionarea in the embodiment shown in FIG. 13 to FIG. 17, for the followingreason:

[0330] That is, before reaching the reflecting surface of the prismsection, luminous flux in the above-described embodiment is bent in thedirection away from the optical axis through the refracting surface andthen reflected by the reflecting surface and subjected to condensingcontrol. This makes it possible to suppress the distance of the partcorresponding to the distance between A and B above to a relativelysmall level. On the contrary, this embodiment has no refracting surfacebefore luminous flux reaches the reflectors 135 and 135′, and thereforethe distance H between A and B above tends to increase, which narrowsthe angle range controllable by the reflectors 135 and 135′.

[0331] A first effect specific to the lighting apparatus of thisembodiment is that the reflecting surfaces are constructed of discretesurfaces of different materials instead of continuous reflectingsurfaces placed in the direction of the irradiation optical axis as inthe case of conventional arts and that a plurality of reflecting layersis placed so as to overlap with one another in the directionperpendicular to the irradiation optical axis.

[0332] Such a configuration makes it possible to significantly reducethe thickness of the lighting optical system in the depth direction,which is the major feature of this embodiment.

[0333] Second, it is possible to significantly reduce the thickness ofthe optical member 134 itself. That is, the configuration essential tothe optical member 134 is only the cylindrical lens surface 134 a havingpositive refracting power in the central area and the peripheralsections 134 b and 134 b′ can have a thin-shaped configuration and theperipheral sections 134 b and 134 b′ with a simple flat shape canfunction sufficiently, which makes it possible to significantly reducethe overall thickness of the optical member 134.

[0334] This makes it possible not only to improve moldability of theoptical member 134 but also to minimize a reduction of light quantitywhen luminous flux passes through a resin material. This alsocontributes to a weight reduction of the image pickup apparatusincorporating this lighting apparatus and other optical equipment.Moreover, since the outermost surface has an extremely simple shape andis constructed of a surface with few optical restrictions, it is easy tosupport the optical member 134 and even when the lighting apparatus ismounted in various optical apparatuses, no special supporting structureis required, which provides a lighting apparatus easy to handle.

[0335] Thirdly, constructing a plurality of reflecting layers withmetallic reflecting surfaces can prevent a problem of a conventionallight guide type electronic flash, that is, a problem that when anoptical member made of a resin optical material is placed close to alight source, the optical member is generally deformed by heat producedby the light source making it impossible to obtain the original opticalcharacteristic depending on the light-emitting condition. That is, byconstructing the reflecting surface close to the light source with ametallic reflecting material, it is possible to prevent deformation ofthe metallic reflecting material caused by heat generated from the lightsource itself, thereby obtain a stable optical characteristic, andfurther widen the space around the light-emitting discharge tube andthereby minimize the influence of radiant heat and convection heatproduced during continuous light emission on the optical member as theresin material.

[0336] Thus, this embodiment makes it possible to construct a small,thin-shaped, extremely efficient lighting optical system with littlelight quantity loss caused by irradiation to the outside of the requiredirradiation range.

[0337] Then, the condensing action of the lighting apparatus accordingto this embodiment in the longitudinal direction of the discharge tube(rightward/leftward direction) will be explained briefly using FIG. 23.

[0338] As shown in FIG. 23, condensing luminous flux in the longitudinaldirection of the discharge tube is conducted by the Fresnel lenssections 134 d and 134 d′ formed on the exit surface side of the opticalmember 134. These Fresnel lens sections 134 d and 134 d′ are only formedin the right and left peripheral sections in the longitudinal directionas shown in the figure and not in the central area. This is because theeffective light-emitting section of the discharge tube 132, which is thelight source, is long in the rightward/leftward directions and evenforming the Fresnel lenses in the central area cannot always condenseluminous flux efficiently.

[0339] On the other hand, for the peripheral sections in thelongitudinal direction where the Fresnel lens sections 134 d and 134 d′are formed, it is possible to limit the direction of luminous fluxemitted from the discharge tube 132 to a certain degree and forming theFresnel lenses in these positions makes it possible to condense luminousflux relatively efficiently.

[0340] This embodiment has described the case where all the luminousflux controlled in areas of three types and five layers of thecylindrical lens surface 134 a provided on the entrance surface side ofthe optical member 134, the peripheral sections 133 b and 133 b′ of thereflector 133 and reflectors 135 and 135′ in the direction (verticaldirection) perpendicular to the longitudinal direction of the dischargetube have light distributions overlapping (matching) with one another,but the setting of this embodiment is not the only one, and it is alsopossible to allow the respective sections to have different lightdistribution characteristics or have asymmetric light distributioncharacteristics in the vertical direction or have different degrees ofcondensing.

[0341] Furthermore, this embodiment has described the case where theoptical member 134 is provided with the cylindrical lens surface 134 a,but the shape of the lens is not limited to such a cylindrical lens andit is also possible to use a toric lens having refracting power also inthe longitudinal direction of the discharge tube or a Fresnel lenshaving equivalent refraction effects.

[0342] As described above, according to the embodiments shown in FIG. 13to FIG. 23, of the luminous flux emitted from the light source invarious directions, it is possible to control irradiation of theluminous flux, which cannot be controlled within the requiredirradiation range by the lens surface of the optical member or thereflection member or the first reflection member, within theabove-described required irradiation range by the reflecting section ofthe optical member or the second reflection member, and it is therebypossible to improve the efficiency of the lighting apparatus byincreasing the effective energy irradiated within the requiredirradiation range.

[0343] Moreover, since a plurality of reflection layers with thereflection member or the first reflection member and reflecting side ofthe optical member or the second reflection member is constructed in thedirection (vertical direction) perpendicular to the irradiation opticalaxis, it is possible to reduce the thickness of the lighting apparatuscompared to the case where one reflection layer is extended in thedirection of the optical axis. Therefore, this lighting apparatus can bemounted on an ultra-thin card type camera or card type electronic flash.

[0344] Furthermore, the shape of the optical member can be simplifiedand slimmed like a simple panel, and therefore even if an optical resinmaterial is used as the material of the optical member, this lightingapparatus is expected to realize sufficient cost reduction such asreducing the molding time or reducing the cost of the die, etc.

[0345] Furthermore, it is possible to freely determine the shapes of thepositive refraction section of the optical member, reflection member orthe first reflection member and the reflecting section of the reflectionmember or the second reflection member, and this lighting apparatus canthereby control the light distributions of this luminous fluxindependently of each other and meticulously. Therefore, it is possibleto easily obtain a desired light distribution within the requiredirradiation range and, for example, easily make the light distributionuniform.

[0346]FIG. 24 to FIG. 27 show a configuration of an optical system of alighting apparatus, which is another embodiment of the presentinvention. FIG. 24 and FIG. 25 are sectional views of theabove-described optical system with the plane including the radialdirection of the discharge tube. FIG. 24 shows a case where theirradiation angle range is small and FIG. 25 shows a case where theirradiation angle range is wide.

[0347]FIG. 26 is a sectional view of the above-described optical systemcut with a plane including the center axis of the discharge tube andFIG. 27 is an exploded perspective view of the above-described opticalsystem. FIG. 24(b) to FIG. 26(b) show traced lines of representativelight emitted from the center of the discharge tube, which is the lightsource, together.

[0348] Furthermore, FIG. 28 also shows a compact camera (a) and cardtype camera (b) incorporating the above-described lighting apparatus.

[0349] As shown in FIG. 28(a) and 28(b), the above-described lightingapparatus is placed at the top of a camera body 411. In these figures,reference numeral 401 denotes a lighting apparatus, 412 denotes apicture-taking lens and 413 denotes a shutter release button.

[0350] In FIG. 28(a), reference numeral 414 denotes an operation memberto zoom the picture-taking lens 412 and depressing this operation memberfrontward allows an image to zoom in and depressing this operationmember backward allows an image to zoom out.

[0351] In FIG. 28(a) and 28(b), reference numeral 415 denotes a modesetting button to switch between various modes of the camera, referencenumeral 416 denotes a liquid crystal display window to inform the userof the operation of the camera, and 417 denotes a light receiving windowof a photometer to measure the brightness of external light and 418denotes an inspection window of a finder.

[0352] Then, the members that determine an optical characteristic of thelighting apparatus will be explained in detail using FIG. 24 to FIG. 27.

[0353] In these figures, reference numeral 302 denotes a discharge tube(xenon tube), which is a cylindrical light source. Reference numeral 303denotes a reflector that reflects luminous flux emitted from thedischarge tube 302 in the irradiation direction (forward) ofilluminating light and is made of a metallic material such as radiantaluminum whose inner surface is formed of a high-reflectance surface ora resin material having an inner surface on which a high-reflectancemetal-evaporated surface is formed.

[0354] Reference numeral 304 denotes a prism-like one-piece opticalmember. On the entrance surface of this optical member 304, a pair ofprism sections are formed. The prism sections made up of refractingsurfaces 304 b, 304 b′ having refracting power in the directionperpendicular (vertical direction) to the longitudinal direction of thedischarge tube 302 and reflecting surfaces 304 c, 304 c′ that almostsatisfy a total reflection condition for the light incident from theserefracting surfaces 304 b, 304 b′ in the upper and lower sides centeredon the optical axis L. Furthermore, as shown in FIG. 26, on the side ofthe exit surface of the optical member 304, a prism array 304 f havingrefracting power in the longitudinal direction (horizontal direction) ofthe discharge tube 302 is formed. As the material of this optical member304, a high transmittance optical resin material such as acrylic resinor glass material is suitable.

[0355] In the above-described configuration, in the case where thecamera is set, for example, to “electronic flash automode”, after theshutter release button 313 is pressed by the user, a control circuit(not shown) decides whether light should be emitted from the lightingapparatus 301 or not based on the brightness of external light measuredby a photometer (not shown), sensitivity of the film loaded or thecharacteristic of an image pickup element such as a CCD or CMOS.

[0356] When the control circuit decides that “light should be emittedfrom the lighting apparatus”, the control circuit outputs alight-emitting signal and allows the discharge tube 302 to emit lightthrough a trigger lead wire attached to the reflector 303.

[0357] Of the luminous flux emitted from the discharge tube 302, theluminous flux component emitted backward or sideward (see FIG. 26) inthe direction of the irradiation optical axis L enters the opticalmember 304 placed in front of the discharge tube 302 through thereflector 303 and the luminous flux component emitted forward in thedirection of the irradiation optical axis directly enters the opticalmember 304 and then both luminous flux components are changed toluminous flux having a predetermined light distribution characteristicthrough the optical member 304 and then irradiated onto an object.

[0358] Hereafter, a setting of an optimal shape in the above-describedlighting apparatus to keep the light distribution characteristic uniformwithin the required irradiation range while extremely slimming the shapeof the lighting optical system in particular will be explained usingFIG. 24 to FIG. 26 more specifically.

[0359] First, a basic concept of changes of the irradiation angle in thevertical direction, which is the radial direction of the discharge tube(direction perpendicular to the longitudinal direction), will beexplained using FIG. 24 and 25. FIG. 24(a) and 24(b) show a statecorresponding to the narrowest irradiation angle range and FIG. 25(a)and 25(b) show a state corresponding to the widest irradiation anglerange.

[0360] (a) and (b) in each figure show the same sectional view and (b)is obtained by adding traced light beams to the sectional view of (a).Reference numerals in the figures correspond to the members in FIG. 26and FIG. 27.

[0361] In these figures, the inner and outer diameters of the glass tubeare shown as the discharge tube 302. In an actual light-emittingphenomenon of this type of discharge tube, light is often emitted fromthe full inner diameter to improve the efficiency and it is reasonableto consider that light is emitted virtually uniformly fromlight-emitting points across the full inner diameter of the dischargetube. However, for simplicity of explanation, suppose the luminous fluxemitted from the center of the light source is representative luminousflux and the figures only show luminous flux emitted from the center ofthe light source. As an actual light distribution characteristic, thelight distribution characteristic as a whole changes in a direction inwhich luminous flux spreads slightly due to luminous flux emitted fromthe periphery of the discharge tube in addition to the representativeluminous flux as shown in the figures, but this luminous flux has almostan identical tendency of light distribution characteristic, andtherefore the following explanations will be based on thisrepresentative luminous flux.

[0362] First, the characteristic shapes of the optical system of theabove-described lighting apparatus will be explained one by one. Theshape of the part of the reflector 303 that covers the back of thedischarge tube 302 is semi-cylindrical (hereinafter referred to as“semi-cylindrical section 303 a”) almost concentric with the dischargetube 302. This is a shape, which is effective to return the lightreflected by the reflector 303 to the vicinity of the center of thelight source again, and has the effect of preventing adverse influencefrom refractions of the glass part of the discharge tube 302.

[0363] Furthermore, such a configuration makes it possible to handle thereflected light from behind the reflector 303 as the outgoing lightalmost equivalent to the direct light from the light source, and therebyit is easy to understand and at the same time convenient because it ispossible to reduce the size of the entire optical system that follows.Furthermore, the reason that the reflector 303 has a semi-cylindricalshape is that if the reflector 303 is smaller than this size, condensingluminous flux directing sideward will require the optical member 304 toextend backward, making it difficult for the prism surface to directluminous flux forward using total reflection, and on the contrary, ifthe reflector 303 is larger than this size, the amount of luminous fluxtrapped inside the reflector 303 will increase and the efficiency willdecrease, both of which are undesirable.

[0364] On the other hand, the upper and lower peripheral sections 303 band 303 b′ of the reflector 303 are shaped like curved surfaces so thatluminous flux emitted from the center of the light source is reflectedby these peripheral sections 303 b and 303 b′ and then led to theperipheral sections 304 d and 304 d′ of the optical member 304. And aswill be explained later, luminous flux refracted through the peripheralsections 304 d and 304 d′ of the optical member 304 provide the mostcondensed light distribution characteristic.

[0365] Furthermore, the areas (hereinafter referred to as “flat surfaceareas”) 303 c and 303 c′ between the semi-cylindrical section 303 a ofthe reflector 303 and the peripheral sections 303 b and 303 b′ areconstructed of flat surfaces almost perpendicular to the optical axis L.

[0366] Then, the detailed shape of the optical member 304 will beexplained. As shown in FIG. 24, the most condensed state is obtainedwhen there is a predetermined distance between the discharge tube 302and the optical member 304.

[0367] First, as shown in FIG. 24(a), the central area through which theoptical axis L passes of the optical member 304 receives a large part ofthe direct light member emitted from the center of the light sourceforming a relatively small angle with the optical axis L and to refractthis member, a non-spherical cylindrical lens surface 304 a is formed inthe center area on the light source side of the optical member 304.

[0368] Then, in the peripheral section of this cylindrical lens surface304 a, refracting surfaces 304 b and 304 b′ to which luminous fluxcomponents emitted from the center of the light source which are notincident on the cylindrical lens surface 304 a and which form arelatively large angle with the optical axis L enter are formed, and inthe area peripheral thereto, reflecting surfaces 304 c and 304 c′ tototally reflect the refracted light which has entered into the prismsection from these refracting surfaces 304 b and 304 b′ are formed.

[0369] In the area peripheral thereto, as described above, refractingsurfaces 304 d and 304 d′ made up of curved surfaces are formed on whichluminous flux reflected by the reflectors 303 b and 303 b′ enters. Thesecylindrical lens surface 304 a, reflectors 303 b, 303 b′, refractingsurfaces 304 d, 304 d′ and reflecting surfaces 304 c, 304 c′ are shapedso that luminous flux emitted from the center of the light source isquasi-parallel to the optical axis L while there is a predetermineddistance between the discharge tube 302 and optical member 304.

[0370] Then, luminous flux incident on the respective sections of theoptical member 304 is refracted or totally reflected to be changed topredetermined angle members and then goes out of the same exit surface304 e.

[0371]FIG. 24(b) shows a light traced lines showing the luminous fluxemitted from the center of the light source and incident on therespective surfaces of the optical member 304 and the light path throughwhich this luminous flux passes. As shown in the figure, almost all theluminous flux emitted from the center of the light source is changed insuch a way as to be parallel to the optical axis. That is, this opticalconfiguration provides the most condensed state.

[0372] On the other hand, it is observed in the optical configurationshown in FIG. 24 that the luminous flux emitted from the center of thelight source goes out of almost the entire exit surface 304 e of theoptical member 304 in the direction quasi-parallel to the optical axisL. In other words, this means that the direction of outgoing light fromthe center of the light source has a one-to-one correspondence with theposition on the exit surface 304 e of the optical member 304 and theoutgoing light is changed without any gap with the given exit surface304 e and parallel to the optical axis, that is, the most efficientcondensing action is performed for the area of aperture of the exitsurface.

[0373] By the way, this figure is obtained by adding only light beams tothe sectional view shown in FIG. 24(a) above and all other shapes arethe same.

[0374] On the other hand, the state shown in FIG. 25 is a state in whichthe discharge tube 302 is placed closer to the optical member 304 thanthe above-described predetermined distance and the optical configurationis set so that the irradiation angle range is widened to a certaindegree. FIG. 25(b) is obtained by adding traced lines of light beamsemitted from the center of the light source to the sectional view inFIG. 25(a) and all the shapes of the different sections of the opticalsystem remain unchanged.

[0375] In such an optical configuration, the edges 304 f and 304 f′formed by an intersection between the refracting surfaces 304 b and 304b′ that determine the light path of the luminous flux totally reflectedby the reflecting surfaces 304 c and 304 c′ and these reflectingsurfaces 304 c and 304 c′ come closer to the flat surface sections 303 cand 303 c′ of the reflector 303. Of the light beams emitted from thecenter of the light source, luminous flux directed from the gap betweenthe reflectors 303 c and 303 c′ and the edges 304 f and 304 f′ of theoptical member 304 toward the peripheral sections 303 b and 303 b′ ofthe reflector 303 is considerably reduced in this way as shown in FIG.25(b).

[0376] The luminous flux component which is originally directed to theperipheral sections 304 d and 304 d′ of the optical member 304 throughthe peripheral sections 303 b and 303 b′ is always the condensed memberto be changed to a member forming a small angle with the direction ofthe optical axis because the light source 302 and reflector 303 aremaintained as one body. However, as described above, since the edges 304f and 304 f′ of the optical member 304 come closer to the flat surfacesections 303 c and 303 c′ of the reflector 303, this member is reducedextremely and directed to the prism section made up of the refractingsurfaces 304 b, 304 b′ and reflecting surfaces 304 c, 304 c′, which isanother light path adjacent thereto. Furthermore, simultaneously withthis, part of the luminous flux controlled by the reflecting surfaces304 c and 304 c′ directly enters into the cylindrical lens surface 304 awhile the discharge tube 302 is separated from the optical member 304and the amount of the luminous flux component incident on thiscylindrical lens surface 304 a also increases.

[0377] Thus, in contrast to the most condensed state shown in FIG. 24 inwhich the system is originally constructed so that flux members of allthe three areas of the refraction area near the optical axis L, thereflection area of the optical member 304 (prism section) peripheralthereto and the reflection area of the reflector 303 further peripheralthereto are condensed, it is possible to gradually change (that is,change the irradiation angle range) the condensed state of each area bychanging the relation of positions between the discharge tube 302 (andreflector 303) and optical member 304 in the direction of the opticalaxis.

[0378] This change in the condensed state will be explained according tothe above-described three areas one by one. First, the refraction areain the optical axis L is constructed of a non-spherical cylindrical lenssurface 304 a with the center of the light source as the focal point torefract luminous flux emitted from the center of the light source in theoptical configuration shown in FIG. 24 so that this luminous fluxbecomes quasi-parallel to the optical axis. In this case, as shown inFIG. 25, when the light source comes close to the cylindrical lenssurface 304 a, a defocused state is generated having the effect ofwidening the irradiation range in all directions. Furthermore, in thestate shown in FIG. 24, part of luminous flux led toward the reflectingsurfaces 304 c and 304 c′ newly enter this area in the state shown inFIG. 25, but this member is also an extension of the luminous fluxcontrolled by the area of this refracted light and is changed to amember with the widest irradiation angle in this refraction area.

[0379] However, since the angle range in this area is an action causedby refraction and therefore no drastic change in the irradiation anglerange is produced for a relatively small amount of movement expectedthis time and as a result, only the light distribution limited to theperiphery of the central area on the irradiation plane is spreaduniformly.

[0380] Then, the reflection area of the optical member 304 (prismsection) will be explained. This area is an area whose irradiation anglerange can be changed drastically by changing the relation of positionsbetween the light source and optical member 304. This is because thechange of the light beam direction by reflection can change theirradiation direction drastically and a reflection phenomenon is used inthe optical member 304 with a high refractive index and therefore agreater angle change can be expected.

[0381] As also shown in FIG. 25(b), the luminous flux component emittedfrom the center of the light source and reflected in this reflectionarea is changed to a member with a certain narrow angle area in theperiphery on the irradiation plane.

[0382] The luminous flux component reflected in this reflection areaseems to be changed only to a member forming a predetermined angle withthe optical axis L in the traced lines of FIG. 25(b), but the lightsource has actually certain dimensions and therefore the reflectionangle range also expands to a certain degree and overlaps with theluminous flux component of the above-described refraction area whenviewed as a whole, and therefore it is possible to obtain a lightdistribution characteristic having an almost uniform angle distributionin a wide angle range.

[0383] Finally, the luminous flux component reflected in the reflectionarea by the outermost reflector 303 gradually decreases as the lightsource comes closer to the optical member 304 from the state in FIG. 24to the state in FIG. 25 as described above.

[0384] However, leaving the reflection member in this reflection area toa certain degree makes it possible to suppress a reduction of theluminous flux component near the optical axis L caused by an increase ofthe luminous flux component through the above-described two reflectionareas and prevent the light quantity near the optical axis L fromreducing.

[0385] Thus, the configuration according to this embodiment can achievea drastic change of the irradiation angle range by a small change in therelation of positions between the light source (discharge tube 302) andoptical member 304 in the direction of the optical axis and at the sametime the members of the three divided areas can compensate for a changein the light distribution characteristic of the respective sections,realizing an optical system which is uniform as a whole and with smalllight quantity loss with respect to the required irradiation range.

[0386] On the other hand, as described above, luminous flux emitted fromthe center of the discharge tube 302 backward is reflected by thesemi-cylindrical section 303 a of the reflector 303, passes through thecenter of the discharge tube 302 again and goes out forward. Thebehavior of the luminous flux thereafter is the same as that shown inFIG. 24(b) and FIG. 25(b).

[0387] Here, an optimal distribution ratio among the three areas of theabove-described refraction area, reflection area of the prism section ofthe optical member 304 and the reflection area of the reflector 303 willbe explained.

[0388] It is basically preferable to construct the basic condensingoptical system with the area of the cylindrical lens surface 304 a andthe reflection area by the peripheral sections 303 b and 303 b′ of thereflector 303 and construct the minimum part bridging between theseareas with the reflection area of the prism section.

[0389] Then, in the most condensed state shown in FIG. 24, it ispreferable that the angle α formed by the luminous flux from the centerof the light source incident on the refracting surfaces 304 b and 304 b′of the prism section with the optical axis L be set to:

20°≦α≦70°  (3)

[0390] Here, if the angle α is smaller than 20°, which is the lowerlimit in Formula (3), forming the reflection area of the prism sectionitself becomes difficult. That is, if the angle α is smaller than 20°,the angles of the prism section edges 304 p and 304 p′ become extremelyacute and at the same time it is necessary to shape the prism sectiondeep in the thickness direction. Thus, it is difficult not only toconstruct but also to manufacture a low-profile optical system.

[0391] On the other hand, when the angle α is greater than 70°, which isthe upper limit of above-described Formula (3), the condensing area bythe reflector 3 decreases and the fact that the reflection area has beendivided into the reflection area of the reflector 303 and the reflectionarea of the prism section itself becomes meaningless, causing variousproblems.

[0392] That is, the distance between the light source and optical member304 necessary to change the illuminating angle decreases, which causes afunctional problem that it is difficult to make a drastic change of theirradiation angle and another problem that manufacturing is difficultbecause the prism section itself of the optical member 304 becomespartially thick and long and the molding time is extended. As an idealmode, it is preferable to narrow this reflection area of the prismsection to a necessary minimum and organize the system in a mode withlittle light quantity loss. Such a configuration makes it possible tominimize the thickness direction, make the configuration of a simpleshape and easy to process.

[0393] For the above-described reasons, this embodiment forms the prismsection according to luminous flux forming an angle with the opticalaxis L within a 30° range from 30° to 60° for optimization.

[0394] Then, optimal shapes of the refracting surfaces 304 b and 304 b′which lead luminous flux to the reflecting surfaces 304 c and 304 c′ ofthe prism sections will be explained. As shown in FIG. 24(a) and 25(b),luminous flux emitted from the center of the light source is largelyrefracted through refracting surfaces 304 b and 304 b′, led in thedirection away from the optical axis L and reach the reflecting surfaces304 c and 304 c′. The ideal shapes of these refracting surfaces 304 band 304 b′ are formed so that the largest possible amount of luminousflux emitted from the light source is led to the reflecting surfaces 304c and 304 c′ and for this purpose, it is necessary to make luminous fluxrefracted abruptly through these refracting surfaces 304 b and 304 b′.

[0395] This also leads to shortening of the length in the direction ofthe optical axis of the reflecting surfaces 304 c and 304 c′, that is,reduction of the size in the thickness direction of the optical system,which also agrees with the object of the present invention. As aspecific shape, it is preferable to construct the refracting surfaces304 b and 304 b′ with flat surfaces whose gradient with respect to theoptical axis L is 0°. However, it is difficult to realize such a flatsurface with a gradient of 0° for reasons related to the processingaccuracy due to the problem of moldability of the optical member. Thisembodiment constructs these refracting surfaces 304 b and 304 b′ withflat surfaces whose gradient with respect to the optical axis L is 10°or less or curved surfaces easy to process.

[0396] On the other hand, constructing a light control area with aplurality of members and arranging them in such a way as to overlap withone another in the direction of the optical axis can obtainunprecedented effects specific to the present invention.

[0397] First, reflecting surfaces (reflecting surfaces 304 c and 304 c′of the prism sections and peripheral sections 303 b and 303 b′ of thereflector 303) are constructed of discrete surfaces made of materials ofdifferent types instead of on continuous surface in the direction of theoptical axis L as in the case of conventional arts and one reflectionmember (reflector 303) is made integrally with the light source and theother reflection member (optical member 304) is made movable withrespect to the light source and these members are placed in such a wayas to overlap with one another in the direction (vertical direction)perpendicular to the optical axis L.

[0398] Such a configuration makes it possible to significantly reducethe thickness of the lighting optical system in the depth direction(direction of the optical axis L), which is the major feature of thepresent invention. That is, as will be explained using the drawings ofthis embodiment, the reflecting surfaces 304 c and 304 c′ of the opticalmember 304 to perform the first reflection are placed first and theperipheral sections 303 b and 303 b′ of the reflector 303 to perform thesecond reflection are placed outside the reflecting surfaces 304 c and304 c′ and in positions overlapping with them in the direction of theoptical axis L, thus making it possible to reduce the thickness of thereflection area in the direction of the optical axis L as a whole.

[0399] Second, it is possible to significantly reduce the thickness ofthe optical member 304 itself. That is, the optical action sectionrequired for the optical member 304 only includes the cylindrical lenssurface 304 a having positive refracting power in the central area, theacute prism sections made up of the refraction surfaces 304 b and 304 b′to separate the direct light from the light source and the lightreflected by the reflector 303 and reflecting surfaces 304 c and 304 c′.Therefore, it is possible to allow the optical member 304 to accomplisha sufficient optical function although it has a simple shape andsignificantly reduce the overall thickness of the optical member 304.

[0400] This makes it possible not only to improve moldability of theoptical member 304 but also to minimize a reduction of light quantitydue to transmittance of the resin material, contributing to a weightreduction of the lighting apparatus and therefore a weight reduction ofthe image pickup apparatus.

[0401] Moreover, the shape of the outermost surface of the opticalmember 304 is extremely simple and is constructed of surfaces with feweroptical restrictions, and therefore it is easy to maintain the opticalmember 304, and even when mounted on an image pickup apparatus, there isno need to adopt any special support structure, providing a mode quiteeasy to handle.

[0402] Third, constructing the reflection area with a plurality ofreflection members can prevent problem with a conventional light guidetype electronic flash, that is, the problem that when an optical membermade of a resin optical material is placed near the light source, heatproduced from the light source melts the optical member, making itimpossible to obtain the original optical characteristic depending onthe light-emitting condition.

[0403] That is, constructing the reflection area with a plurality ofreflecting surfaces makes it possible to place the edges 304 f and 304f′, which is a boundary between the refracting surface and reflectingsurface of the optical member 304 which is most vulnerable to heat, awayfrom the light source and also expand the space around the dischargetube 302, and therefore it is possible to minimize influences on resinmaterials of radiant heat and convection heat produced during continuouslight emissions and prevent deterioration of the optical characteristic.

[0404] Thus, this embodiment can construct a small and extremelyefficient lighting optical system of a variable irradiation angle typewith little light quantity loss due to irradiation to the outside of therequired irradiation range, even using a fewer members such as thereflector 303 and optical member 304.

[0405] Next, a condensing action of this embodiment in the longitudinaldirection of the discharge tube 302 will be explained using FIG. 26.

[0406]FIG. 26 shows a sectional view of the optical system cut with aplane including the center axis of the discharge tube 302. FIG. 26(a)and FIG. 26(b) show the same sectional view and FIG. 26(b) shows atraced lines of light from the center of the light source together.

[0407] As shown in the figure, the side of the optical member 304 fromwhich luminous flux goes out is constructed of a prism array 304 fformed in the central area which through the optical axis L passes withboth slopes having almost the same angle and acute Fresnel lens sections304 g and 304 g′ formed in the area peripheral to the prism array 304 f.

[0408] Furthermore, side reflectors 303 d and 303 d′ molded as one bodywith the reflector 303 are provided on both sides of the optical member304. These side reflectors 303 d and 303 d′ are intended to reflect partof luminous flux emitted from the discharge tube 302, which escapessideward instead of entering the optical member 304, or unnecessarymembers of reflected light generated at the prism array 304 f andFresnel lens sections 304 g and 304 g′ formed on the side of the exitsurface of the optical member 304 and allow these light members toreenter from the sides 304 h and 304 h′ of the optical member 304 to usethese light members effectively.

[0409] This embodiment sets the apex angle of the prism array 304 f inthe central area to a constant angle of 105°. The prism array 304 f withsuch an angle setting has the effect of allowing a luminous fluxcomponent with a relatively large angle of incidence (luminous fluxcomponent with the angle of incidence on the optical member 304 ranging30° to 40°) to go out of the exit surface with the same angle at whichlight is refracted through the entrance surface, that is, the effect ofallowing a luminous flux component to go out of the exit surface underlittle influence of refraction on the exit surface, and the effect ofcondensing incident luminous flux to luminous flux within a certainrange of irradiation angle.

[0410] The apex angle of this prism array 304 f is not limited to 105°and if it is set to a smaller angle, for example, 90°, it is possible tonarrow the angle range of luminous flux going out of the optical member304. On the contrary, if the apex angle is set to a greater angle, forexample, 120°, it is also possible to widen the angle distribution ofluminous flux going out of the optical member 304.

[0411] On the other hand, as shown in FIG. 26(b), there are also someoutgoing luminous flux components reaching the prism array 304 f, whichare reflected by this prism array 304 f and returned to the light sourceagain. These luminous flux components are reflected by the reflector 303and enter the optical member 304 again, are changed to predeterminedangle members by the prism array 304 f or Fresnel lenses 304 g and 304g′ and then irradiated onto an object.

[0412] Thus, most of luminous flux emitted from the center of the lightsource is changed to luminous flux with a certain angle distribution andgoes out of the optical member 304. The light distribution in this caseis solely dependent on the angle setting of the prism array 304 f and isnot affected by the pitch, etc. of the prism array. This allows theoptical member 304 to perform condensing control in an extremely shallowarea without requiring the depth in the direction of the optical axismaking it possible to drastically reduce the overall size (thickness) ofthe optical system with respect to the direction of the optical axis.

[0413] Furthermore, as shown in the figure, Fresnel lens sections 304 gand 304 g′ with acute angles are formed on the periphery of the opticalmember 304. Though the optical member 304 is considerably thin, thisperipheral area is an area where luminous flux with certain directivityis obtained and forming the Fresnel lens in this area allows efficientcondensing action.

[0414] From the figure, no conspicuous condensing operation isobservable. This is because only luminous flux emitted from the centerof the light source is shown and a considerable amount of luminous fluxemitted from around the terminals on both sides of the discharge tube302 is changed to luminous flux components that concentrate on theirradiation optical axis.

[0415] Thus, determining the shape of the plane of outgoing light of theoptical member 304 allows even an extremely thin optical system placednear the light source to condense luminous flux to a certain angle rangeefficiently.

[0416] Furthermore, the light distribution with respect to thelongitudinal direction (horizontal direction) of the discharge tube 302is determined by a condensing action by the prism array 304 f on theside of the exit surface of the optical member 304 or Fresnel lenssurfaces 304 g and 304 g′ and the light distribution in the directionperpendicular to the longitudinal direction (vertical direction) of thedischarge tube 302 is determined by a highly efficient condensing actionby the refraction area of the cylindrical lens surface 304 a provided onthe light source side (side of the entrance surface) of the opticalmember 304, the reflection area of the reflector 303 and the reflectionarea of the prism section of the optical member 304 provided at somemidpoint between these two areas. Therefore, this embodiment can providean unprecedentedly thin lighting optical system with an excellentoptical characteristic.

[0417]FIG. 29 and FIG. 30 show examples of the light distributioncharacteristic obtained by the lighting optical system configured asshown above.

[0418] The light distribution characteristic shown in FIG. 29 is a lightdistribution characteristic corresponding to the optical configurationshown in FIG. 24 in the most condensed state. The light distributioncharacteristic shown in FIG. 30 is the light distribution characteristiccorresponding to the optical configuration shown in FIG. 25 in the mostdiffused state.

[0419] The configuration shown in the figure can make a drastic changein the irradiation angle with respect to the vertical direction.Furthermore, it is also possible to obtain an almost uniform lightdistribution characteristic with respect to the required irradiationangle range.

[0420] In the state shown in FIG. 24, it might also be possible to shapeeach surface so that all luminous flux emitted from the center of thelight source is quasi-parallel to the optical axis of outgoing light sothat luminous flux can be condensed within the narrower angle range thanthe light distribution characteristic shown in FIG. 29. However, thelight distribution characteristic actually has a certain degree ofextension due to the size of the light source itself. As shown in FIG.29, the irradiation angle determined by a half value of the illuminanceof the central area extends up to 12°.

[0421] Furthermore, in the diffused state shown in FIG. 30, the halfvalue irradiation angle extends up to 34°, almost three times theabove-described angle.

[0422] On the other hand, with respect to the horizontal direction, nodrastic angle change is observed for reasons related to theconfiguration of the optical system. However, the angle range in thediffused state corresponding to FIG. 25 is slightly wider than the anglerange in the condensed state corresponding to FIG. 24. This may beattributable to the fact that while the condensed or diffused state nearthe central area drastically changes according to a change in lightdistribution in the vertical direction, the distribution in theperipheral sections does not change drastically, and as a result, it isunderstood that a relative change takes place in this irradiation anglerange.

[0423] This embodiment has described a lighting apparatus that performslight distribution control in the direction perpendicular to thelongitudinal direction of the discharge tube 302 by changing therelative distance between the light source and the optical member 304and changing the irradiation angle range using three types and fivelayers of the cylindrical lens surface 304 a provided on the lightsource side, the peripheral sections 303 b and 303 b′ of the reflector303, and reflecting surfaces 304 c and 304 c′ using the most condensedstate shown in FIG. 24 as the standard. However, the present inventionis not limited to this embodiment and the reference state need not beset to a state in which luminous flux of all areas is condensed most.

[0424] This is because the light source has dimensions of a certainvalue or greater and the distance between each condensing control planeand the light source varies and it may be convenient not to set thelight distribution in a reference state to the one in the most condensedstate but to differentiate the reference state from the most condensedstate.

[0425] As an example of this, when the light source is large, theirradiation angle from the cylindrical lens surface near the lightsource tends to extend considerably. Especially, luminous flux emittedfrom ahead of the center of the light source has this strong tendency ofspreading and even the most condensing optical configuration cannot besaid to include no luminous flux toward the outside of the requiredirradiation range.

[0426] On the other hand, suppose the degree of condensing of theluminous flux member controlled by the reflector at the positionfarthest from the light source does not decrease even if the size of thelight source increases to a certain degree and its distribution does notdeviate from the initially set irradiation angle distributionconsiderably.

[0427] From this, by shaping the cylindrical lens surface whose controlsurface exists near the light source so that the focal point is formedat a position closer to the object than the center of the light source,it is possible to prevent the distribution of luminous flux going outthrough this cylindrical lens surface from spreading more thannecessary.

[0428] Furthermore, also in the case where the irradiation angle rangeis changed with prime importance attached to the wide angle side wherethe most condensed state is not always necessary, it may be moreconvenient to determine the shape of each surface so that a relativelywider light distribution characteristic is obtained instead of settingthe light distribution to the most condensed state uniformly withrespect to luminous flux controlled by the reflectors other than thecylindrical lens surface in the center and the reflecting surfaces ofthe prism section.

[0429] Furthermore, this embodiment has described the case where theconfiguration of each surface on the light source (entrance surface)side and the configuration of each surface on the side of the exitsurface are symmetric with respect to the optical axis, but thisembodiment is not limited to such a symmetric shape. For example, thereflecting surfaces 304 c and 304 c′ of the optical member 304 areconstructed symmetrical on both sides of the optical axis, but thereflecting surfaces 304 c and 304 c′ need not always be formed in suchsymmetric positions, but can also be placed asymmetrically. This is notonly true for the reflecting surfaces but also for the shape of thereflector and shape of the cylindrical lens surface in the central area.

[0430] Furthermore, also with respect to the prism array in the centralarea formed on the side of the exit surface light, it is also possibleto provide a variation in the light distribution characteristic in thehorizontal direction using a prism array having different angle settingsfor right and left. Furthermore, with respect to the Fresnel lenssection in the periphery, it is also possible to provide a variation forthe degree of condensing and provide a variation for the overall lightdistribution characteristic.

[0431] Furthermore, this embodiment has described the case where thecylindrical lens surface 304 a formed in the central area of the opticalmember 304 is non-spherical, but this cylindrical lens surface is notlimited to a non-spherical shape but can be a cylindrical shape. Also,this cylindrical lens can have a toric lens surface considering thecondensing performance in the longitudinal direction of the dischargetube 302.

[0432]FIG. 31 to FIG. 34 show a configuration of an optical system of alighting apparatus, which is another embodiment of the presentinvention. FIG. 31 and FIG. 32 are sectional views of theabove-described optical system with the plane including the radialdirection of the discharge tube and FIG. 31 shows the case with a narrowirradiation angle range and FIG. 32 shows the case with a wideirradiation angle range.

[0433] Furthermore, FIG. 33 is a sectional view of the above-describedoptical system cut with a plane including the center axis of thedischarge tube and FIG. 34 is an exploded perspective view of theabove-described optical system. FIG. 31(b) and FIG. 32(b) also showtraced lines of representative light beams emitted from the center ofthe discharge tube which is the light source.

[0434] Furthermore, the above-described lighting apparatus is mounted inthe compact camera (a) and card type camera (b) shown in FIG. 28.

[0435] This embodiment is a lighting optical system giving priority tothe light distribution characteristic obtained by widening theirradiation angle range shown in FIG. 32 and constructed so that themost excellent light distribution characteristic is obtained regardingthis state as a standard.

[0436] In the above-described figures, reference numeral 302 denotes acylindrical discharge tube (xenon tube), which is a light source.Reference numeral 323 denotes a reflector that reflects luminous fluxemitted from the discharge tube 302 in the irradiation direction(forward) of the illuminating light. This reflector has ahigh-reflectance inner surface made of a metallic material such asradiant aluminum or a resin material having an inner surface on which ahigh-reflectance metal-evaporated surface is formed.

[0437] Reference numeral 324 is a prism-like one-piece optical member.On the entrance surface side of the optical member, there is a pluralityof prism pairs made up of refracting surfaces 324 b, 324 d, 324 f, 324h, 324 b′, 324 d′, 324 f′, 324 h′ having refracting power in thedirection quasi-perpendicular (vertical direction) to the longitudinaldirection of the discharge tube 302 and reflecting surfaces 324 c, 324e, 324 g, 324 i, 324 c′, 324 e′, 324 g′, 324 i′ that almost satisfy atotal reflection condition with respect to the light incident from theserefracting surfaces, on the upper and lower sides centered on theoptical axis L.

[0438] Furthermore, as shown in FIG. 33, Fresnel lens sections 324 q and324 q′ having refracting power in the longitudinal direction (horizontaldirection) of the discharge tube 302 are formed on the right and leftperipheries on the side of the exit surface light of the optical member324.

[0439] As the material of this optical member 324, high transmittanceoptical resin material such as acrylic resin, etc. or glass material issuitable.

[0440] This embodiment is a lighting optical system designed to bethinner than the embodiments shown in FIG. 24 to FIG. 27 and capable ofobtaining large variations in the irradiation angle while keeping thelight distribution characteristic uniformly within the requiredirradiation range and with a minimum amount of positional change betweenthe light source and optical member. Setting of an optimal shape of eachmember of this lighting optical system will be explained using FIG. 31to FIG. 34 in detail below.

[0441] First, a basic concept of an irradiation angle change in thevertical direction, which is the radial direction (the directionperpendicular to the longitudinal direction) of the discharge tube, willbe explained using FIG. 31 and FIG. 32. Here, FIG. 31(a) and 31(b) showa state corresponding to the narrowest irradiation angle range and FIG.32(a) and 32(b) show a state corresponding to the widest irradiationangle range.

[0442] (a) and (b) of each figure show a sectional view of the lightingapparatus cut with the same section and (b) is obtained by adding tracedlight beams to the sectional view of (a). Reference numerals in thefigures correspond to the members in FIG. 33 and FIG. 34.

[0443] Furthermore, in these figures, for the same reason in theembodiments shown in FIG. 24 to 27, luminous flux emitted from thecenter of the light source is regarded as representative luminous fluxand the figures only show luminous flux emitted from the center of thelight source. As an actual light distribution characteristic, the lightdistribution characteristic as a whole changes in a direction in whichluminous flux spreads slightly due to luminous flux emitted from theperiphery of the discharge tube 302 in addition to the representativeluminous flux as shown in the figures, but this luminous flux has almostan identical tendency of light distribution characteristic, andtherefore the following explanations will be based on thisrepresentative luminous flux.

[0444] First, the characteristic shapes of the optical system of theabove-described lighting apparatus will be explained one by one. Theshape of the part of the reflector 323 that covers the back of thedischarge tube 302 is semi-cylindrical (hereinafter referred to as“semi-cylindrical section 323 a”) almost concentric with the dischargetube 302. This is a shape, which is effective to return the lightreflected by the reflector 323 to the vicinity of the center of thelight source again, and has the effect of preventing adverse influencefrom refractions of the glass part of the discharge tube 302.

[0445] On the other hand, the peripheral sections 323 b and 323 b′ thatextend in the vertical direction of this reflector 323 have curvedsurface shapes so that luminous flux emitted from the center of thelight source is reflected by these peripheral sections and led to slopes(324 j, 324 j′) formed in the peripheral sections of the optical member324. Furthermore, as will be described later, these peripheral sectionsare formed so that luminous flux refracted through the peripheralsections 324 j and 324 j′ of the optical member 324 has a lightdistribution characteristic condensed to a certain degree.

[0446] Furthermore, the areas (hereinafter referred to as “flat surfaceareas”) 323 c and 323 c′ between the semi-cylindrical section 323 a ofthe reflector 323 and the peripheral sections 323 b and 323 b′ areconstructed of flat surfaces almost perpendicular to the optical axis L.

[0447] Then, the detailed shape of the optical member 324 which has thelargest influence on the light distribution characteristic of thelighting apparatus of this embodiment will be explained. FIG. 31 shows astate in which there is a predetermined distance between the dischargetube 302 and the optical member 324 so that the shape and opticalconfiguration of each section are set to obtain a predeterminedcondensed state.

[0448] First, as shown in FIG. 31(a), on the optical member 324, thecentral area through which the optical axis passes is an area whichreceives more direct incident light members forming a relatively smallangle with the optical axis L of luminous flux emitted from the centerof the light source, and to refract these members, a cylindrical lenssurface 324 a, which consists of part of a cylindrical surface, isformed in the optical member 324 facing the light source in the centralarea.

[0449] Then, outside this cylindrical lens surface 324 a, there arerefracting surfaces 324 b and 324 b′ to receive more luminous fluxmembers not incident on the cylindrical lens surface 324 a and forming aslightly large angle with the optical axis L of the luminous fluxemitted from the center of the light source and behind these refractingsurfaces 324 b and 324 b′, there are reflecting surfaces 324 c and 324c′ which almost satisfy total reflection conditions for this refractedlight. Up to thispoint, this optical system is almost the same as theoptical system of the embodiment described in FIG. 24 to FIG. 27.

[0450] A feature of this embodiment is that there is not only one pairbut a plurality of pairs of prism sections made up of these refractingsurfaces 324 b and 324 b′ and reflecting surfaces 324 c and 324 c′ inthe upper and lower sides. That is, outside one pair of upper and lowerprism sections made up of refracting surfaces 324 b, 324 b′ andreflecting surfaces 324 c, 324 c′ provided near the optical axis L,there is another pair of upper and lower prism sections made up ofrefracting surfaces 324 d, 324 d′ and reflecting surfaces 324 e, 324 e′,and outside these prism sections, there is a further pair of upper andlower prism sections made up of refracting surfaces 324 f, 324 f′ andreflecting surfaces 324 g, 324 g′, and outside these prism sections,there is a still further pair of upper and lower prism sections made upof refracting surfaces 324 h, 324 h′ and reflecting surface 324 i, 324i′.

[0451] Then, the respective reflecting surfaces 324 c, 324 c′, 324 e,324 e′, 324 g, 324 g′, 324 i, 324 i′ are shaped so that luminous fluxreflected here has a light distribution characteristic of apredetermined condensed state.

[0452] Furthermore, as described above, in the area peripheral to theoutermost prism sections of the optical member 324 facing the lightsource, there are inclined surfaces 324 j and 324 j′ which receive theluminous flux reflected by the peripheral sections 323 b and 323 b′ ofreflector 323. The shapes of the peripheral sections 323 b and 323 b′ ofthis reflector 323 and the above-described inclined surfaces (refractingsurfaces) 324 j and 324 j′ are also determined so as to obtain a lightdistribution characteristic of a predetermined condensed state as in thecase of the light path via the above-described prism sections.

[0453] Luminous flux incident on different sections of the opticalmember 324 is changed to predetermined angle members by refractions andreflections and then goes out of the same exit surface 324 k.

[0454] Thus, forming a plurality of prism section pairs on the opticalmember 324 as multiple layers in the vertical direction centered on theoptical axis L has an advantage of significantly reducing the depth inthe direction of the optical axis of the lighting optical system. At thesame time, when applied to a lighting apparatus, which allows theirradiation angle to be variable, this embodiment also has an advantageof significantly reducing the amount of change in the relation ofpositions in the direction of the optical axis between the light sourceand optical member 324 when changing the irradiation angle. This can besaid to be an extremely effective mode in realizing a lighting opticalsystem of a variable irradiation angle type with a minimum volume, whichis extremely thin, yet capable of obtaining a desired light distributioncharacteristic.

[0455]FIG. 31(b) is a light traced lines showing how luminous fluxemitted from the center of the light source passes through each surfaceof the optical member 324 and what light path the luminous flux takes.As shown in the figure, most luminous flux emitted from the center ofthe light source is changed to members forming a relatively small anglewith the optical axis L. That is, it is possible to obtain the mostcondensed state in the optical system of this embodiment using thisoptical configuration.

[0456] On the other hand, FIG. 32 shows a state in which the dischargetube 302 is placed close to the optical member 324, which provides awider irradiation angle range than the state shown in FIG. 31. Thisembodiment adjusts the light distribution characteristic in this stateto a light distribution characteristic when a wide angle lens is mountedand optimizes the system so as to obtain the most uniform lightdistribution characteristic and regards this state as the designstandard state.

[0457] In such an optical configuration, edges 324 l, 324 l′, 324 m, 324m′, 324 n, 324 n′, 324 o and 324 o′ come closer to the flat surfacesections 323 c and 323 c′ of the reflector 323, which consist ofintersections between the refracting surfaces and reflecting surfaces ofthe respective prism sections. Thus, when the optical member 324 comescloser to the reflector 323, the amount of the luminous flux componentemitted from the center of the light source and incident on thecylindrical lens surface 324 a increases as shown in FIG. 32(b), whilethe amount of luminous flux component which would originally be directedto the peripheral sections 323 b and 323 b′ of the reflector 323 isdecreased significantly.

[0458] More specifically, since the discharge tube 302 and the reflector323 are maintained as one body, the members originally directed to theperipheral sections 324 j and 324 j′ of the optical member 324 throughthese peripheral sections 323 b and 323 b′ are the members which shouldalways be condensed to a small range of angle formed with the directionof the optical axis. However, as described above, the edges 324 o and324 o′ of the optical member 324 come closer, and therefore thesemembers are reduced extremely and allocated to different prism sectionsadjacent there to one by one. At the same time, while the optical member324 is away from the reflector 323, part of luminous flux controlled bythe reflecting surfaces 324 c and 324 c′ directly enters the cylindricallens surface 324 a formed in the central area through which the opticalaxis L passes and the ratio of the luminous flux components incident onthis cylindrical lens surface 324 a increases.

[0459] Thus, as opposed to the original configuration in the condensedstate in FIG. 31 in which luminous flux of three areas; the refractionarea in the central area, the reflection area of the optical member 324(prism section) peripheral thereto and the reflection area of thereflector 323 on the outermost periphery is condensed to a certainrange, this embodiment can gradually change the condensed state of eacharea above by allowing the light-emitting section made up of the lightsource and reflector 323 and the optical member 324 to come closer indirection of the optical axis L. This is not only because thisphenomenon can change, through reflections, the orientation of theluminous flux component whose outgoing direction would be controlledthrough refractions in the previous state and can drastically change theirradiation direction, but also because this reflection phenomenon ishandled in the optical member 324 with a higher refractive index, andtherefore a greater angle change can be expected.

[0460] This reflection component of light is changed to a member in acertain narrow angle area in the periphery on the irradiation plane asshown in FIG. 32(b). In the traced lines of light in FIG. 32(b), thisreflection member seems to be changed to only a predetermined anglemember in a certain direction, but actually the light source has acertain dimension, and therefore the angle area extends to a certainarea and also overlaps with the member in the refraction area in thecentral area, and therefore it is possible to obtain a lightdistribution characteristic having an almost uniform angle distributionover a wide angle range as a whole.

[0461] Furthermore, the luminous flux component in the reflection areaof the reflector 323 is reduced gradually as the light source andoptical member 324 come closer. Here, leaving a certain amount of theluminous flux component of this reflection area makes it possible tosuppress a reduction of the light component forming a small angle withthe direction of the optical axis and prevent luminous flux near theoptical axis from reducing in the light distribution characteristic, andtherefore it is effective to leave a certain amount of this member.

[0462] Thus, the configuration of this embodiment can drastically changethe irradiation angle range by making a small change to the relation ofpositions between the light source and optical member 324 in thedirection of the optical axis L, and at the same time allow luminousflux components of multiple areas to compensate for changed distributioncharacteristics and thereby realize a uniform optical system with littlelight quantity loss with respect to the required irradiation range as awhole.

[0463] Especially, placing a plurality of layers of prism sections inthe direction (vertical direction) perpendicular to the direction of theoptical axis makes it possible to realize a lighting optical system witha significantly reduced depth in the direction of the optical axis.

[0464] According to the configuration of this embodiment, it is possibleto reduce the maximum dimensions of the optical system in the directionof the optical axis shown in FIG. 31 to 4.9 mm, smaller than 5 mm. Onthe other hand, the state with the widest irradiation angle shown inFIG. 32 is realized by making a change as small as 0.6 mm to therelation of positions between the light source and optical member 324 inthe direction of the optical axis L compared to the state in FIG. 31.

[0465] Thus, since the configuration of this embodiment allows a drasticchange of the irradiation angle range with a fewer members, theconfiguration of this embodiment includes the following advantages:

[0466] 1. Light from the light source can be irradiated without manyparts, and therefore higher efficiency is achieved.

[0467] 2. Ultra-miniaturization is possible though the system is alsoequipped with the function of changing the irradiation angle range.

[0468] 3. A cost reduction is possible.

[0469] Then, an optimal distribution ratio between three areas; theabove-described refraction area, reflection area of the prism sectionsand reflection area of reflector 323, will be explained.

[0470] Basically, the largest feature of this embodiment is that aplurality of reflecting surfaces of the prism section is formed andplaced in such a way as to overlap with one another in the form oflayers in the direction perpendicular to the optical axis to minimizethe thickness of the optical system in the direction of the opticalaxis. Thus, unlike the concept of the embodiments shown in FIG. 24 toFIG. 27, the way for extending the reflection area of the plurality oflayers of prism sections determines the extent to which the thickness ofthe lighting apparatus can be reduced.

[0471] Furthermore, in the most condensed state shown in FIG. 31, it ispreferable that the angle α, which is an angle that luminous fluxincident on the refracting surface of this prism section from the centerof the light source forms with the optical axis L be:

20°≦α80°  (4)

[0472] Here, if the angle α is smaller than 20°, which is the lowerlimit of the above-described Formula (4), forming the reflection area ofthe prism section itself becomes difficult. That is, the angle of theedges of the prism section itself becomes considerably acute and at thesame time it is necessary to form a shape deep in the thicknessdirection of the prism section. This makes it difficult not only toconstruct but also to manufacture a thin- shaped optical system, whichis the main subject of the present invention, and is therefore notdesirable. On the other hand, if the angle α is larger than 80°, whichis the upper limit, the ratio of the luminous flux component condensedby the reflector 323 decreases resulting in a reduction of the amount ofluminous flux directed toward the central area with the widenedirradiation angle, making it impossible to always obtain a uniform lightdistribution characteristic.

[0473] For the above-described reasons, this embodiment forms aplurality of prism section pairs corresponding to luminous flux formingan angle with the optical axis L within an approximately 50° range from25° to 75° for optimization.

[0474] As an ideal mode, it is preferable to widen this reflection areaby this prism section wherever possible and this allows a configurationwith dimensions in the thickness direction of the optical member 324reduced most, making it possible to realize an ultra-thin-shaped opticalsystem, reduce the time for molding the optical member 324 with a resinmaterial, providing an inexpensive and easy to process mode.

[0475] Then, optimal shapes of refracting surfaces 324 b, 324 b′, 324 d,324 d′, 324 f, 324 f′, 324 h and 324 h′ which lead luminous flux in theprism section to reflecting surfaces 324 c, 324 c′, 324 e, 324 e′, 324g, 324 g′, 324 i and 324 i′ will be explained. As is apparent from thelight traced lines shown in FIG. 31(b) and 32(b), luminous flux emittedfrom the center of the light source is refracted through the respectiverefracting surfaces a great deal, directed in the direction away fromthe optical axis L and reaches the reflecting surface of the same prismsection.

[0476] An ideal shape of this refracting surface have a configurationleading the largest possible ratio of luminous flux emitted from thelight source to the reflecting surfaces and for this purpose it isnecessary to drastically refract light through this refracting surface.This also leads to reducing the length of each reflecting surface in thedirection of the optical axis L, that is, reducing dimensions of theoptical system in the thickness direction, which also agrees with thesubject of the present invention.

[0477] As a specific shape, it is preferable that the refractingsurfaces 324 b, 324 b′, 324 d, 324 d′, 324 f, 324 f′, 324 h and 324 h′be flat surfaces having a gradient of 0° with respect to the opticalaxis L. However, it is difficult to form a flat surface having agradient of 0° for reasons related to the moldability and processingaccuracy of the optical member. Taking into account the processingcondition, this embodiment constructs these refracting surfaces 324 b,324 b′, 324 d, 324 d′, 324 f, 324 f′, 324 h and 324 h′ with flatsurfaces having a gradient of 10° or less with respect to the opticalaxis L or with curved surfaces which are easy to process.

[0478] On the other hand, this embodiment can achieve unprecedentedeffects specific to the present invention by constructing reflectionareas made up of a plurality of prism sections for a single opticalmember and changing the relation of positions between this opticalmember and light source.

[0479] First, it is possible to minimize the volume required for thelighting optical system of a variable irradiation angle type. That is,instead of constructing the reflecting surfaces with a conventionalsingle curved surface (reflector or reflecting surface) continuous inthe direction of the optical axis, this embodiment constructs thereflecting surfaces with a plurality of discrete reflecting surfacesutilizing total reflection and places the plurality of reflectingsurfaces in such a way as to overlap with one another in the directionperpendicular to the optical axis. Constructing the reflecting surfacesin this way can significantly reduce the thickness in the depthdirection (the direction of the optical axis L) of the lighting opticalsystem and minimize the volume necessary for the lighting opticalsystem.

[0480] According to FIG. 31 and FIG. 32, the reflecting surfaces 324 cand 324 c′ are placed near the optical axis first and the reflectingsurfaces 324 e and 324 e′ are placed at positions peripheral to thereflecting surfaces 324 c and 324 c′ and overlapping them in thedirection of the optical axis. Likewise, this embodiment adopts aconfiguration significantly reducing the thickness of the reflectingsurface in the direction of the optical axis as a whole by placing thereflecting surfaces 324 g, 324 g′ and 324 i, 324 i′ so that theirpositions in the direction of the optical axis L overlap with oneanother.

[0481] Second, since the optical member 324 is of a thin-shaped type, ithas excellent moldability and can be manufactured at a low cost. Thatis, the optical action section required for the optical member 324 isonly the cylindrical lens surface 324 a having positive refracting powerin the central area and a plurality of prism sections with acute anglesmade up of refracting surfaces and reflecting surfaces. Therefore,though having a simple shape, the optical member 324 can performsufficient optical functions making it possible to significantly reducethe thickness of the optical member 324 as a whole.

[0482] This not only improves moldability of the optical member 324using resin but also minimizes a reduction of light quantity due to thetransmittance of the resin material and also contributes to a reductionof weight of the lighting apparatus and therefore a reduction of weightof the image pickup apparatus.

[0483] Furthermore, the shape of the outermost plane of the opticalmember 324 is quite simple and constructed of a surface with few opticalrestrictions, and therefore it is easy to maintain the optical member324 and there is no need to adopt a special support structure even whenmounted on an image pickup apparatus and it is a mode quite easy tohandle.

[0484] Third, constructing a reflecting area with a plurality ofreflection members can prevent a problem of a conventional light guidetype electronic flash, that is, a problem that when an optical membermade of a resin optical material is placed close to a light source, theoptical member is generally melted by heat produced by the light sourcemaking it impossible to obtain the original optical characteristicdepending on the light-emitting condition.

[0485] That is, by constructing a reflecting area with a plurality ofreflecting surfaces, it is possible to place the edges 324 l and 324 l′,which is a boundary between the refracting surface and reflectingsurface of the optical member 324 which is most vulnerable to heat, awayfrom the light source. Furthermore, it is also possible to expand thespace around the discharge tube 302. This minimizes the influence ofradiant heat and convection heat produced during continuous lightemission on the resin material and prevents deterioration of the opticalcharacteristic.

[0486] Thus, it is possible to construct a small and highly efficientlighting optical system of a variable irradiation angle with little lossof light quantity due to irradiation toward the outside of the requiredirradiation range using a small number of members of only the reflector323 and optical member 324.

[0487] Then, a condensing action in the longitudinal direction of thedischarge tube 302 according to this embodiment will be explained usingFIG. 33.

[0488] As shown in the figure, this embodiment forms a flat surfacesection 324 p in the central area of the outgoing light side of theoptical member 324 and provides Fresnel lens sections 324 q and 324 q′in the peripheral sections to provide a predetermined light distributioncharacteristic.

[0489] Here, though the optical member 324 has a considerablythin-shaped configuration, the peripheral sections near the terminalsections at the right and left ends of the discharge tube 302 are areaswhere certain luminous flux directivity exists. Furthermore, forming theFresnel lens sections 324 q and 324 q′ in this area makes it possible togenerate a relatively good condensing action.

[0490] On the other hand, in the central area of the exit surface, theflat surface section 324 p is constructed for the following reason. Thatis, for a lighting optical system in which the irradiation angle ischanged within a wide view angle range according to a relatively wideangle lens as shown in this embodiment, it is possible to realizeuniform irradiation using a flat plane rather than a complicated planeconfiguration to condense luminous flux for areas near the optical axiswhere it is difficult to control luminous flux.

[0491] Determining the shape of each section of the outgoing light sideof the optical member 324 makes it possible to uniformly and efficientlycondense outgoing luminous flux within a certain angle range althoughthis is quite a thin-shaped optical system with the optical member 324placed close to the light source.

[0492] Thus, this embodiment performs condensing control for thelongitudinal direction (horizontal direction) of the discharge tube 302by using Fresnel lens sections 324 q and 324 q′ on the outgoing lightside of the optical member 324 and performs condensing control for thedirection perpendicular (vertical direction) to the longitudinaldirection of the discharge tube 302 by using the cylindrical lenssurface 324 a and reflector 323 provided on the light source side of theoptical member 324 and a plurality of reflecting surfaces (prismsections) of the optical member 324 placed at a some midpoint betweenthese two areas, and can thereby provide an ultra-thin lighting opticalsystem with an excellent optical characteristic unprecedented by theprevious arts.

[0493] As shown above, this embodiment performs light distributioncontrol in the direction perpendicular to the longitudinal direction ofthe light source by changing the relative distance between the lightsource and the optical member 324 and changing the irradiation anglerange using areas of three types and 11 layers of the cylindrical lenssurface 324 a provided on the light source side, the reflector 323 andreflecting surfaces of a plurality of prism section pairs.

[0494] Moreover, as shown in this embodiment, the present invention issufficiently applicable to an optical system that makes a change of theirradiation angle giving priority to the light distributioncharacteristic on the wide angle side, and is also applicable to alighting optical system provided with a required condensing action bymoving the optical member 324 and light source in the direction so as toincrease the distance between them by a predetermined amount using thisstate as the reference.

[0495] Furthermore, this embodiment has presented examples of caseswhere all the configurations of the light source planes and theconfigurations of the outgoing light planes are symmetric with respectto the optical axis, but the present invention is not limited to suchsymmetric configurations. For example, it is also possible to place thereflecting surfaces of the prism section of the optical member 324asymmetrically with respect to the optical axis or the number ofreflecting surfaces may vary between the upper side and lower side ofthe optical axis. Furthermore, it is possible to provide asymmetricshapes not only for the above-described reflecting surfaces but also forthe reflector and the cylindrical lens surface. Likewise, with respectto the Fresnel lens surfaces formed on the plane of outgoing light side,it is possible to provide variations for the light distributioncharacteristic in the horizontal direction using Fresnel lenses withdifferent angle settings on the right and left.

[0496] Furthermore, the cylindrical lens surface 324 a formed in thecentral area of the optical member 324 is constructed of part of thecylindrical surface, but can also be non-spherical or toric lenssurface, taking into account the condensing performance in thelongitudinal direction of the light source.

[0497]FIG. 35 and FIG. 36 show a configuration of an optical system of alighting apparatus, which is another embodiment of the presentinvention. FIG. 35 shows a condensed state with the narrowed irradiationangle range and FIG. 36 shows a diffused state with the widenedirradiation angle range. This embodiment is a lighting optical systemthat gives priority to the light distribution characteristic with thenarrowed irradiation angle range shown in FIG. 35 and determines theshape of each section so that the characteristic with the most excellentcondensing performance is obtained in this condition. Furthermore, FIG.35(b) and FIG. 36(b) also show light traced lines of representativelight beams emitted from the center of the light source together.

[0498] Furthermore, the above-described lighting apparatus is mounted inthe compact camera (a) and card type camera (b) shown in FIG. 28.

[0499] In the above-described figures, reference numeral 302 denotes acylindrical discharge tube (xenon tube) which is a light source.Reference numeral 333 denotes a semi-cylindrical reflector that reflectsluminous flux emitted from the discharge tube 302 forward. Thisreflector has a high-reflectance inner surface made of a metallicmaterial such as radiant aluminum or a resin material having an innersurface on which a high-reflectance metal-evaporated surface is formed.

[0500] Reference numeral 334 is an optical member provided with aplurality of prism section pairs made up of refracting surfaces havingrefracting power in the direction quasi-perpendicular to thelongitudinal direction (vertical direction) of the discharge tube 302and reflecting surfaces on entrance surface. As the material of thisoptical member 334, high transmittance optical resin material such asacrylic resin, etc. or glass material is suitable.

[0501] This embodiment is capable of making large changes of theirradiation angle while significantly reducing the thickness of theoverall shape of the lighting optical system, keeping the lightdistribution characteristic within the required irradiation rangeuniformly and with a minimum amount of positional change between thelight source and optical member 334 and the largest difference from theembodiments shown in FIG. 24 to FIG. 27 is that this embodiment performslight distribution control using a total reflection action of theoptical member 334 without wrapping around the peripheral sections ofthe reflector 333 behind the optical member 334.

[0502] The shape of the discharge tube 302 in the axial direction is thesame as that of the discharge tube 302 according to the embodiments inFIG. 24 to 27 and FIG. 31 to 34. An optimal shape of the lightingoptical system according to this embodiment will be explained using FIG.35 and FIG. 36 in detail below.

[0503]FIG. 35 and FIG. 36 show a basic concept of making a change of theirradiation angle in the vertical direction according to thisembodiment. Here, FIG. 35(a) and 35(b) show a state corresponding to thenarrowest irradiation angle range and FIG. 36(a) and 36(b) show a statecorresponding to the widest irradiation angle range. (a) and (b) in thefigures are drawings of the same section.

[0504] Furthermore, for simplicity of explanation, for the same reasonsexplained in the embodiments in FIG. 24 to 27, these figures show onlyluminous flux emitted from the center of the light source asrepresentative luminous flux.

[0505] First, the characteristic shape of the above-described lightingoptical system will be explained one by one. Reflector 333 is formed soas to cover the back of the discharge tube 302 and the shape issemi-cylindrical almost concentric with the discharge tube 302. This isattributable to the same reason explained in the embodiment described inFIG. 24 to FIG. 27.

[0506] Then, the detailed shape of the optical member 334 will beexplained. FIG. 35 shows a state in which there is a predetermineddistance between the discharge tube 302 and optical member 334 and thisis the most condensed state obtained in this embodiment.

[0507] As shown in FIG. 35(a), in the central area through which theoptical axis L passes on the light source side of the optical member334, a non-spherical cylindrical lens surface 334 a is formed to refractthe direct light member of luminous flux emitted from the center of thelight source, which forms a relatively small angle with the optical axisL. Because of the non-spherical shape of this cylindrical lens surface334 a, luminous flux emitted from the center of the light source isrefracted so that the luminous flux emitted from the center of the lightsource becomes quasi-parallel to the optical axis L with respect to thissection.

[0508] In the area peripheral to the cylindrical lens surface 334 a, aplurality of prism section pairs made up of refracting surfaces 334 b,334 b′, 334 d, 334 d′, 334 f, 334 f′, 334 h and 334 h′ to receiveincident luminous flux components forming a relatively large angle withthe optical axis without passing through the cylindrical lens surface334 a out of the luminous flux emitted from the center of the lightsource and reflecting surfaces 334 c, 334 c′, 334 e, 334 e′, 334 g, 334g′, 334 i and 334 i′ that satisfy almost the total reflection conditionfor the light members incident from the respective refracting surfaces,in the vertical direction centered on the optical axis L.

[0509] Then, the reflecting surfaces 334 c, 334 c′, 334 e, 334 e′, 334g, 334 g′, 334 i and 334 i′ are shaped so that luminous flux reflectedhere is in a predetermined condensed state.

[0510] Thus, the luminous flux incident on the respective sections ofthe optical member 334 is refracted or totally reflected by the opticalmember 334 and then goes out of the same exit surface 334 j.

[0511] Since this embodiment places a plurality of prism section pairsin such a way as to overlap with one another in the vertical directionperpendicular to the optical axis L on the light source side of theoptical member 334, this embodiment has an advantage of significantlyreducing the depth in the direction of the optical axis L of thelighting optical system. When this configuration is applied to thelighting optical system whose irradiation angle can be changed, thisembodiment also has an advantage of significantly reducing the amount ofchange of the relation of positions in the direction of the optical axisL between the light source and optical member 334 when the irradiationangle is changed. This is extremely effective in realizing a lightingoptical system of a variable irradiation angle type with a minimumvolume capable of achieving a desired light distribution characteristicdespite a very thin configuration.

[0512] Furthermore, since this embodiment has no peripheral sections ofthe reflectors located outermost with respect to the optical axis L andno light path through refractions of the optical member shown in FIG. 24to FIG. 27, and FIG. 31 to FIG. 34, it is possible to obtain a stableoptical characteristic easily without the need to consider the accuracyof positioning between the reflector and the optical member or mutualinterference between the reflector and optical member.

[0513]FIG. 35(b) is a light traced drawing showing what light path istaken by luminous flux emitted from the center of the light source andincident on the respective surfaces of the optical member 334. As shownin the figure, most of luminous flux emitted from the center of thelight source is changed so as to be almost parallel to the optical axisL. That is, the most condensed state can be realized with this opticalconfiguration in the optical system of this embodiment.

[0514] On the other hand, FIG. 36 shows the discharge tube 302 placedcloser to the optical member 334 compared to the state shown in FIG. 35and the optical configuration is set so as to extend the irradiationangle range by a predetermined amount. In this embodiment, the lightdistribution characteristic in this state corresponds to the lightdistribution characteristic when a wide angle lens is mounted.

[0515] First, in the case of such an optical configuration, the edges334 k and 334 k′ formed of an intersection between the refractingsurfaces 334 b, 334 b′ and reflecting surfaces 334 c, 334 c′ come closerto the reflector 333. Thus, as the optical member 334 comes closer tothe reflector 333, the member of light emitted from the center of thelight source and incident on the cylindrical lens surface 334 aincreases as shown in FIG. 36(b), while the amount of luminous fluxincident on the refracting surfaces 334 h, 334 h′ of the peripheralsections of the optical member 334 is extremely reduced.

[0516] Thus, in the condensed state shown in FIG. 35 while the allluminous flux from the refraction area in the central area and thereflection area of the prism sections peripheral thereto isquasi-parallel to the optical axis. And as described in FIG. 36, it ispossible to gradually change the condensed state of light from theabove-described areas by allowing the light-emitting section made up ofthe light source and reflector 333 and the optical member 334 to comecloser in the direction of the optical axis L.

[0517] This makes it possible to make a drastic change of theirradiation angle range with a small change to the relative positionsbetween the light source and optical member 334 in the direction of theoptical axis. Especially placing a plurality of reflecting surfaces ofthe prism sections so as to overlap one another from the optical axisside to the peripheral side makes it possible to realize a lightingoptical system having an extremely small depth in the direction of theoptical axis L.

[0518] This embodiment forms four layers of reflecting surfaces in boththe upper and lower sides of the optical member 334, but the presentinvention is not limited to the four layers of reflecting surfaces. Asthe number of layers of reflecting surfaces increases, it is possible toconstruct a thinner optical system.

[0519] Furthermore, to reduce the overall size of the optical system, itis also necessary to consider the pitch of reflecting surfaces inaddition to multiple layers of reflecting surfaces. This embodiment isdesigned to achieve balance in the overall shape by segmenting the pitchof reflecting layers in the area close to the cylindrical lens surface334 a formed in the central area of the optical member 334 and wideningthis pitch toward the periphery for the following reasons:

[0520] First, from the relation of positions between the light sourceand the respective refracting surfaces that lead luminous flux to thereflecting surfaces, as the angle of incidence on each refractingsurface changes and the luminous flux goes away from the optical axis L,the angle of incidence decreases. This is also apparent from FIG. 35(b)and light incident on the refracting surface 334 b near the optical axishas a considerably large angle of incidence, while light incident on therefracting surface 334 h in the peripheral section has a smaller angleof incidence. Thus, the difference in the angle of incidence of lightincident on each refracting surface also has a considerable influence onthe shape of the reflecting surface provided for this refractingsurface.

[0521] That is, for the refracting surface having an acute angle ofincidence, it is necessary to form the reflecting surface which isdeeper, that is, the reflecting surface which extends to the exitsurface side. However, extending the reflecting surface in this waymakes it more difficult to reduce the thickness of the lighting opticalsystem in the direction of the optical axis, which is the greatestobject of the present invention.

[0522] Thus, to avoid this problem, this embodiment narrows the area ofincidence on the refracting surface near the optical axis where luminousflux has a large angle of incidence. In other words, this embodimentnarrows the pitch of the prism section near the optical axis to preventthe reflecting surface from exceeding a predetermined depth.

[0523] For this reason, by narrowing the pitch of the prism section nearthe optical axis and widening the pitch of the prism section in theperiphery, it is possible to maintain the position in the direction ofthe optical axis at the end of the reflecting surface on the entrancesurface side almost constant and reduce the thickness of the opticalmember. For the same reason, by increasing the number of reflectingsurfaces, it is possible to reduce the depth of the reflecting surfacesand reduce the overall thickness of the optical member. Therefore, if itis intended to reduce the overall size of the optical system to aminimum, it is desirable to narrow this pitch.

[0524] By the way, when the number of reflecting surfaces increases, theminiaturization in the direction of the optical axis may be achieved,but the dimensions in the vertical direction perpendicular to the theoptical axis L increases. Thus, this embodiment prevents thisunnecessary expansion of dimensions by widening the pitch of thereflecting surfaces as the distance from the optical axis L increases.Especially, this embodiment prevents expansion of dimensions in thedirection perpendicular to the optical axis by covering the layers ofthe outermost refracting surfaces 334 h, 334 h′ and reflecting surfaces334 i, 334 i′ up to a large angle range with respect to the lightsource.

[0525] This embodiment has described the case where the opticalcharacteristic is optimized with respect to the optical member 334 withfour layers of reflecting surfaces, and this embodiment also attains areduction of dimensions in the vertical direction through theabove-described measure that minimizes the thickness in the direction ofthe optical axis L.

[0526] The effects specific to this embodiment include the following:

[0527] First, this configuration is very simple. As the reflector 333, aminimum semi-cylindrical reflector concentric with the discharge tube302, which is the light source, can be used. Furthermore, with respectto a change to the irradiation angle range, it is possible to realize alighting optical system whose irradiation angle range can be changed byonly changing the relation of positions between the light source andoptical member 334 with a very simple configuration.

[0528] Second, this embodiment can irradiate an object with luminousflux emitted from the light source very efficiently. This embodimentperforms light distribution control on all luminous flux emitted fromthe light source forward (including luminous flux reflected by thereflector 333) through refractions or reflections by the optical member334. Thus, this embodiment can efficiently lead luminous flux comparedto reflections on metallic surfaces of conventional reflectors and canalso use limited energy effectively.

[0529] Third, this embodiment can form a wide range of air layer on theperiphery between the reflector 333 and optical member 334. In aconventional light guide electronic flash, a resin material is oftenplaced near the light source, which causes a problem that heat generatedfrom the light source deforms the optical member, making it impossibleto obtain the original optical characteristic depending on thelight-emitting condition. Adopting the configuration of this embodimentcan also expand a space around the discharge tube, minimize influencesof radiant heat and convection heat generated during continuous lightemission on the resin material and prevent deterioration of the opticalcharacteristic.

[0530]FIG. 37 and FIG. 38 show the configuration of an optical system ofa lighting apparatus, which is another embodiment of the presentinvention. This embodiment is a mode in which the embodiments shown inFIG. 35 and FIG. 36 are partially changed. FIG. 37 shows a condensedstate with the narrowed irradiation angle range and FIG. 38 shows adiffused state with the widened irradiation angle range. This embodimentis a lighting optical system giving priority to the light distributioncharacteristic obtained by narrowing the irradiation angle range shownin FIG. 37 and determines the shapes of the respective sections so thatthe most excellent condensing characteristic is obtained in this state.FIG. 37(b) and FIG. 38(b) also show light traced lines of representativelight beams emitted from the center of the light source together.

[0531] In the above-described figures, reference numeral 302 denotes acylindrical discharge tube (xenon tube) which is a light source.Reference numeral 333 denotes a semi-cylindrical reflector that reflectsluminous flux emitted from the discharge tube 302 forward.

[0532] Reference numeral 344 is an optical member provided with aplurality of prism section pairs made up of refracting surfaces havingrefracting power in the vertical direction perpendicular to thelongitudinal direction of the discharge tube 302 on the entrance surfaceand reflecting surfaces, and a reflector 345 is fixed thereto as onebody. This reflector 345 is intended to construct reflecting surfaceshaving the functions equivalent to those of the outermost prism sections(334 h, 334 i) in the embodiments shown in FIG. 35 and FIG. 36. Thereflecting surface of this reflector 345 is constructed of aparaboloidal metallic reflecting surface. Furthermore, as the materialof the optical member 344, a high transmittance optical resin materialsuch as acrylic resin or glass material is suitable.

[0533] This embodiment is capable of obtaining large changes of theirradiation angle while significantly reducing the thickness of theoverall shape of the lighting optical system of an image pickupapparatus in particular, keeping the light distribution characteristicwithin the required irradiation range uniformly with a minimum amount ofpositional change between the light source and optical member 344 andthe reflector 345 in the direction of the optical axis L. The largestdifference from the embodiments in FIG. 35 and FIG. 36 above is thatpart of the reflecting surface of the optical member is replaced by areflection member.

[0534] The shape of the discharge tube 302 in the axial direction is thesame as that in the embodiments in FIG. 24 to FIG. 27 and FIG. 31 toFIG. 34. An optimal shape of the lighting optical system according tothis embodiment will be explained in detail below.

[0535]FIG. 37 and FIG. 38 show a basic concept of making a change of theirradiation angle in the vertical direction. Here, FIG. 37(a) and 37(b)show a state corresponding to the narrowest irradiation angle range andFIG. 38(a) and 38(b) show a state corresponding to the widestirradiation angle range. (a) and (b) in the figures are drawings of thesame section. (b) is a light traced lines added to the sectional view in(a).

[0536] Furthermore, for simplicity of explanation, for the same reasonsexplained in the first embodiments, FIG. 37(b) and FIG. 38(b) show onlyluminous flux emitted from the center of the light source asrepresentative luminous flux.

[0537] Here, of the optical configuration, mainly the differences fromthe embodiments in FIG. 35 and FIG. 36 will be explained. FIG. 37 showsa state in which there is a predetermined distance between the dischargetube 302 and optical member 344 and the most condensed state is obtainedin this embodiment.

[0538] As shown in FIG. 37(a), a cylindrical lens surface 344 a in thecentral area through which the optical axis passes and three prismsection pairs peripheral thereto (constructed of refracting surfaces 344b, 344 d, 344 f, 344 b′, 344 d′, 344 f′ and reflecting surface 344 c,344 e, 344 g, 344 c′, 344 e′, 344 g′) have almost the same shapes asthose in the embodiments in FIG. 35 and FIG. 36. The outermost area ofthe optical member 345 is constructed of flat surface sections 344 h and344 h′ in this embodiment.

[0539] Furthermore, reflection members 345 are formed as one body withthe optical member 344 on the side of flat surface sections 344 h and344 h′ facing the light source. The reflection members 345 have aparaboloidal plane whose focal point is the center of the light sourceso that luminous flux emitted from the center of the light source ischanged to luminous flux quasi-parallel to the optical axis in the mostcondensed state shown in FIG. 37.

[0540] Determining the shapes of members in this way, this embodimentcan provide almost the same optical characteristic as that of the thirdembodiment. In the state of the widest irradiation angle shown in FIG.38, the reflector 345 functions so as to widen the irradiation anglerange having almost the same effects as those of the embodiments in FIG.35 and FIG. 36.

[0541] Here, the reason that this embodiment uses the reflectors 345formed as one body with the optical member 344 will be explained.

[0542] The first reason is that the outermost area including thereflecting surface 334 i is a part having the largest thickness of theoptical member 334 in the embodiments in FIG. 35 and FIG. 36, which canrequire more time to mold the optical member 344 and cause a costincrease. That is, this embodiment aims at making the overall thicknessof the optical member 344 uniform to shorten the molding time.

[0543] This embodiment uses reflectors with a metallic reflectingsurface as the reflectors 345 giving the highest priority to the cost,but the present invention is not limited to this mode. It is possible toprovide a similar optical characteristic using a method of using theseperipheral sections not as prisms but as the reflecting surfaces, thatis, a method of constructing the reflecting surfaces with a thinmaterial and using part of the material as a evaporated surface orconstructing the reflecting surfaces with a high-reflectance thinmaterial pasted instead of using a high-reflectance reflector.

[0544] The second reason is that this embodiment aims at reducing theweight of the optical member. The weight of the optical member largelydepends on this outermost prism section and it is one of objects toreduce the weight of this part.

[0545] As shown above, this embodiment provides three pairs ofreflecting surfaces (prism sections) for the optical member 344 and apair of reflectors 345 peripheral thereto, constructing an opticalsystem having four layers of reflecting surfaces in both the upper andlower sides as a whole, but the present invention is not limited to suchan optical system having four layers. For example, it is also possibleto provide two or more layers of reflectors or form inner reflectingsurfaces, instead of outermost reflecting surfaces, using reflectors. Asthe number of reflecting surfaces increases, it is possible to constructa thinner optical system. As explained in the embodiments in FIG. 35 andFIG. 36, it is also possible to change the pitch of reflecting surfaces.

[0546]FIG. 39 and FIG. 40 show a configuration of a lighting apparatus,which is another embodiment of the present invention. This embodiment isan example of modification to the above-described embodiments in FIG. 24to 27. FIG. 39 is an exploded perspective view of the optical system ofthe lighting apparatus and FIG. 40 is a rear view of only the opticalmember. Since light traced drawings and light distributioncharacteristics, etc. are almost the same as those of the otherembodiments, and so detailed explanations thereof will be omitted.

[0547] This embodiment consists of two pairs of reflecting surfaces ofthe lighting optical system of the lighting apparatus explained in theembodiments in FIG. 24 to FIG. 27 and the optical member 354 with theshape on the entrance surface side modified three-dimensionally. Thisembodiment aims at mainly improving the light distributioncharacteristic toward four corners on the surface of the object.

[0548] The operation of changing the irradiation angle is performed bymaintaining the discharge tube 352 and the reflector 353 as one body asin the case of the embodiments shown in FIG. 24 to FIG. 38 and changingthe relation of positions between these members and the optical member354 in the direction of the optical axis. The change of the irradiationangle range is the same as for the other embodiments.

[0549] In FIG. 39 and FIG. 40, reference numeral 352 denotes acylindrical light source which is a light source, 353 denotes areflector and 354 denotes a one-piece prism-like optical member. Thefunctions of these members are almost equivalent to those of theembodiments in FIG. 24 to FIG. 27, but this embodiment is characterizedby the shape of each surface on the discharge tube 352 side of theoptical member 354.

[0550] In the same figure, the part of the reflector 353 covering theback of the discharge tube 352 is formed semi-cylindrical (hereinafterreferred to as “semi-cylindrical section 353 a”) almost concentric withthe discharge tube 352 and further includes toric surface 353 b, 353 b′covering the back of the outermost reflecting surfaces 354 e, 354 e′ inthe vertical direction of the optical member 354 and flat surfacesections 353 c, 353 c′ connecting these toric surfaces 353 b, 353 b′ andsemi-cylindrical section 353 a.

[0551] On the other hand, a lens surface 354 a having positiverefracting power in the direction perpendicular to the optical axis(vertical direction) is formed in the central area through which theoptical axis passes on the entrance surface side of the optical member354 and two layers each for upper and lower side (two pairs) of prismsections made up of refracting surfaces and reflecting surfaces areformed on the periphery on the entrance surface side.

[0552] This embodiment is different from the embodiments in FIG. 24 toFIG. 27 in that the lens surface 354 a in the central area andreflecting surfaces 354 c, 354 c′, 354 e, 354 e′ in the periphery areconstructed of three-dimensional curved surfaces.

[0553] More specifically, a toric surface is formed as the lens surface354 a in the central area and conical first refracting surfaces 354 b,354 b′ making up the prism section and toric-surfaced first reflectingsurfaces 354 c, 354 c′ are formed symmetrically with respect to theoptical axis in the vertical direction in the area peripheral to theabove-described toric surface.

[0554] In the area further peripheral thereto, conical second refractingsurfaces 354 d, 354 d′ making up the prism section and toric-surfacedsecond reflecting surfaces 354 e, 354 e′ are formed symmetrically withrespect to the optical axis in the vertical direction. Furthermore, aplurality of prism arrays is formed on the plane of outgoing light 354h.

[0555] A condensing operation and effect of shaping the optical member354 in this way will be explained.

[0556] First, between the center of the lens surface and the peripheralsections of right and left direction, the toric lens surface 354 adeforms gradually, its width in the vertical direction decreases andrefracting power in the direction perpendicular to the optical axis(vertical direction) at each position in the horizontal direction alsochanges gradually.

[0557] This makes the overall light distribution characteristic uniformand prevents variations of light distribution on the irradiation surfaceof an object, which are likely to occur on the boundary edge between therefracting surface and reflecting surface of the prism section.

[0558] Furthermore, constructing not only the central area with a toricsurface but also constructing the reflecting surfaces 354 c, 354 c′, 354e, 354 e′ in the peripheral sections with toric surfaces whose sectionalshape in the horizontal and vertical directions changes graduallyaccording to the position makes it possible to make the lightdistribution characteristic up to four corners of the irradiation rangeuniform.

[0559] Thus, this embodiment can construct a lighting optical systemwith a highly condensed light distribution with a narrow irradiationangle range as a whole by actions of the toric lens surface 354 a andthe reflecting surfaces as two pairs of toric surfaces with respect tothe luminous flux emitted from the center of the discharge tube 352.

[0560] Furthermore, segmenting the reflecting surfaces of the opticalmember 354 into smaller portions than the conventional arts and placingthose segments in the vertical direction makes it possible to reduce thethickness of the optical member 354 as in the case of theabove-described embodiments in FIG. 24 to FIG. 38. Moreover, since theboundary edge between the refracting surface and reflecting surface ofthe prism section goes away from the center of the light source, it ispossible to prevent the optical resin material from being affected byradiant heat from the light source and reduce adverse influences on theoptical characteristic.

[0561] Furthermore, using a toric-surfaced configuration for the lenssurfaces and each reflecting surface, this embodiment has a specificeffect of making it possible to easily construct a lighting opticalsystem with a uniform light distribution characteristic toward fourcorners in the irradiation range without any additional special opticalsystem.

[0562] As described above, the above-described embodiments in FIG. 24 toFIG. 30 can provide a lighting apparatus capable of drastically reducingthe thickness of the system compared to the conventional variable rangetype lighting apparatus and using energy from the light source with highefficiency and obtaining a uniform light distribution characteristic onthe irradiation surface.

[0563] Furthermore, this embodiment can provide a thin-shaped lightingapparatus capable of obtaining a uniform light distributioncharacteristic by providing a pair or a plurality of pairs of reflectionsections arranged in the direction perpendicular to the optical axiswithin the plane including the radial direction of the light sourcecentered on the optical axis.

[0564] Furthermore, by setting angle α formed by light emitted from thecenter of the light source and incident on the above-describedreflecting sections with the optical axis within the range:

20°≦α≦70°

[0565] this embodiment can reduce both the thickness and the size in thevertical direction of the lighting apparatus at the same time.

[0566] Then, the above-described lighting apparatus can be mounted on asmall image pickup apparatus, especially a card type image pickupapparatus as a lighting apparatus whose irradiation range can bechanged.

What is claimed is:
 1. A lighting apparatus comprising: a light source;an optical member which is placed in front of said light source andprovided with a reflecting surface to reflect light from said lightsource forward; wherein said optical member includes a plurality ofpairs of said reflecting surfaces arranged on both sides of the opticalaxis within a plane including the radial direction of said light sourcein the direction perpendicular to the optical axis.
 2. The lightingapparatus according to claim 1, wherein said optical member comprises aprism section provided with a refracting surface that receives lightincident from said light source and a reflecting surface that reflectsthe light incident from the refracting surface, and a plurality of pairsof said prism sections are formed on said optical member, arranged onboth sides of the optical axis within the plane including the radialdirection of said light source in the direction perpendicular to theoptical axis.
 3. The lighting apparatus according to claim 1, wherein alens section having positive refracting power is formed on and close tothe optical axis on the entrance surface side of said optical member andsaid plurality of reflecting surface pairs is formed in the peripheralsection.
 4. The lighting apparatus according to claim 1, wherein saidlight source has a cylindrical shape, and a prism array havingrefracting power in the longitudinal direction of said light source isformed on the exit surface side of said optical member.
 5. The lightingapparatus according to claim 1, wherein said reflecting surface is acurved surface.
 6. The lighting apparatus according to claim 2, whereinan edge in said light source side formed by an intersection between saidrefracting surface and said reflecting surface of each of prism sectionis located closer to said light source side for a prism section which isfarther from the optical axis in the direction perpendicular to theoptical axis within the plane including the radial direction of saidlight source.
 7. The lighting apparatus according to claim 2, whereinsaid edges of a pair of prism sections of said plurality of prismsection pairs, farthest from the optical axis within the plane includingthe radial direction of said light source in the direction perpendicularto the optical axis is placed substantially in the same position as thecenter position of said light source in the direction of the opticalaxis.
 8. The lighting apparatus according to claim 2, further comprisinga reflection member which is placed behind said light source and whichreflects light from said light source forward, wherein said reflectionmember extends to a position to cover at least part of the reflectingsurface of a pair of prism sections of said plurality pairs of prismsections, farthest from the optical axis within the plane including theradial direction of said light source in the direction perpendicular tothe optical axis.
 9. The lighting apparatus according to claim 3,wherein each of said reflecting surface is shaped in such a way that theirradiation range of light irradiated through each of said reflectingsurface and the irradiation range of light irradiated through said lenssection substantially overlap with each other.
 10. The lightingapparatus according to claim 1, wherein the irradiation range of lightirradiated from said optical member is made variable by changing arelation of positions in the direction of the optical axis between saidlight source and said optical member.
 11. An image pickup apparatuscomprising: a light source; and an optical member which is placed infront of said light source and provided with a reflecting surface thatreflects light from said light source forward, wherein a plurality ofpairs of said reflecting surfaces is formed on said optical member,arranged on both sides of the optical axis within a plane including theradial direction of said light source in the direction perpendicular tothe optical axis.
 12. The image pickup apparatus according to claim 11,wherein said optical member comprises a prism section provided with arefracting surface that receives light incident from said light sourceand a reflecting surface that reflects the light incident from saidrefracting surface, and a plurality of pairs of said prism sections isformed on said optical member, arranged on both sides of the opticalaxis within the plane including the radial direction of said lightsource in the direction perpendicular to the optical axis.
 13. The imagepickup apparatus according to claim 11, wherein a lens section havingpositive refracting power is formed on and close to the optical axis onthe entrance surface side of said optical member and said plurality ofreflecting surface pairs is formed in the peripheral section.
 14. Theimage pickup apparatus according to claim 11, wherein said light sourcehas a cylindrical shape, and a prism array having refracting power inthe longitudinal direction of said light source is formed on the exitsurface side of said optical member.
 15. The image pickup apparatusaccording to claim 11, wherein said reflecting surface is a curvedsurface.
 16. The image pickup apparatus according to claim 12, whereinan edge in said light source side formed by an intersection between saidrefracting surface and said reflecting surface of each prism section islocated closer to said light source side for a prism section which isfarther from the optical axis in the direction perpendicular to theoptical axis within the plane including the radial direction of saidlight source.
 17. The image pickup apparatus according to claim 12,wherein said edges of a pair of prism sections of said plurality ofprism section pairs, farthest from the optical axis within the planeincluding the radial direction of said light source in the directionperpendicular to the optical axis is placed substantially in the sameposition as the center position of said light source in the direction ofthe optical axis.
 18. The image pickup apparatus according to claim 12,further comprising a reflection member which is placed behind said lightsource and which reflects light from said light source forward, whereinsaid reflection member extends to a position to cover at least part ofthe reflecting surface of a pair of prism sections of said pluralitypairs of prism sections, farthest from the optical axis within the planeincluding the radial direction of said light source in the directionperpendicular to the optical axis.
 19. The image pickup apparatusaccording to claim 13, wherein each of said reflecting surface is shapedin such a way that the irradiation range of light irradiated througheach of said reflecting surface and the irradiation range of lightirradiated through said lens substantially overlap with each other. 20.The image pickup apparatus according to claim 11, having a card typeconfiguration.
 21. The image pickup apparatus according to claim 11,wherein the irradiation range of light irradiated from said opticalmember is made variable by changing a relation of positions in thedirection of the optical axis between said light source and said opticalmember.
 22. A lighting apparatus comprising: a light source; an opticalmember which is placed in front of said light source; and a reflectionmember which is placed in such a way as to cover the back of said lightsource and a front space between said light source and said opticalmember, and reflects light irradiated from said light source forward,wherein said optical member comprises: a lens section which is placed onand close to the optical axis on the entrance surface side of saidoptical member and has positive refracting power; and a reflectingsection which is placed to peripheral side of said lens section,provided closer to the optical axis than the area through which thelight reflected by the part of said reflection member covering saidfront space passes, and reflects light from said light source forward.23. The lighting apparatus according to claim 22, wherein saidreflecting section is shaped like a prism having a refracting surfacethat receives light incident from said light source and a reflectingsurface that reflects light incident from said refracting surface. 24.The lighting apparatus according to claim 22, wherein the refractingsurface of said reflecting section is constructed of a flat surfacewhose gradient with respect to the optical axis is 4° or less.
 25. Thelighting apparatus according to claim 22, wherein the reflecting surfaceof said reflecting section is constructed of a flat surface or curvedsurface.
 26. The lighting apparatus according to claim 22, wherein apair or a plurality of pairs of said reflecting sections is provided onboth sides of the optical axis.
 27. The lighting apparatus according toclaim 22, wherein said reflecting section is shaped in such a way thatthe irradiation range of light irradiated through said reflectingsection and the irradiation range of light irradiated through said lenssection and said reflection member substantially overlap with eachother.
 28. The lighting apparatus according to claim 22, wherein anangle α formed by light emitted from the center of said light source andincident on said reflecting section with respect to the optical axis isincluded in a range of 20°≦α≦70°.
 29. The lighting apparatus accordingto claim 22, wherein the area covering said front space of saidreflection member is a curved surface of the second order.
 30. Thelighting apparatus according to claim 22, wherein the area covering saidfront space of said reflection member is a semi-ellipsoidal curvedsurface whose focal point coincides with the center of said lightsource.
 31. The lighting apparatus according to claim 22, wherein saidlight source has a cylindrical shape and the lens section of saidoptical member is a cylindrical lens or toric lens having positiverefracting power within the plane perpendicular to the longitudinaldirection of said light source.
 32. The lighting apparatus according toclaim 22, wherein the irradiation range of light irradiated from saidoptical member is made variable by changing a relation of positions inthe direction of the optical axis between said light source and saidoptical member.
 33. A lighting apparatus comprising: a light source; anoptical member which is placed in front of said light source andprovided with a lens section having positive refracting power and beingplaced on and close to the optical axis on the entrance surface side ofthis optical member; a first reflection member which is placed in such away as to cover the back of said light source and a front space betweensaid light source and said optical member and reflects light emittedfrom said light source forward; and a second reflection member which isplaced to peripheral side of said lens section near the entrance surfaceof said optical member and provided closer to the optical axis than thearea through which the light reflected by the part of said firstreflection member covering said front space passes and reflects lightfrom said light source forward.
 34. The lighting apparatus according toclaim 33, wherein said second reflection member is constructed of a flatsurface or curved surface.
 35. The lighting apparatus according to claim33, wherein a pair or a plurality of pairs of said second reflectionmembers is provided on both sides of the optical axis.
 36. The lightingapparatus according to claim 33, wherein said second reflection memberis shaped in such a way that the irradiation range of light irradiatedthrough said second reflection member and the irradiation range of lightirradiated through said lens section and said first reflection membersubstantially overlap with each other.
 37. The lighting apparatusaccording to claim 33, wherein an angle α formed by the light emittedfrom the center of said light source and incident on said secondreflection member with respect to the optical axis is within a range of20°≦α≦70°.
 38. The lighting apparatus according to claim 33, whereinsaid light source has a cylindrical shape and the area of said firstreflection member covering the back of said light source is shaped likea semi-cylinder concentric with said light source.
 39. The lightingapparatus according to claim 33, wherein the area of said firstreflection member covering said front space is a curved surface ofsecond order.
 40. The lighting apparatus according to claim 33, whereinthe area of said first reflection member covering said front space is asemi-ellipsoidal curved surface whose focal point coincides with thecenter of said light source.
 41. The lighting apparatus according toclaim 33, wherein said light source has a cylindrical shape and the lenssection of said optical member is a cylindrical lens or toric lenshaving positive refracting power within the plane perpendicular to thelongitudinal direction of said light source.
 42. The lighting apparatusaccording to claim 33, wherein the irradiation range of light emittedfrom said optical member is made variable by changing a relation ofpositions between said light source, said optical member and said secondreflection member in the direction of the optical axis.
 43. An imagepickup apparatus comprising: a light source; an optical member which isplaced in front of said light source; and a reflection member which isplaced in such a way as to cover the back of said light source and afront space between said light source and said optical member andreflects light emitted from said light source forward, wherein saidoptical member comprises: a lens section which is placed on and close tothe optical axis on the entrance surface side of said optical member andhas positive refracting power; and a reflecting section which is placedto peripheral side of said lens section and closer to the optical axisthan the area through which the light reflected by the part of saidreflection member covering said front space passes, and reflects lightfrom said light source forward.
 44. The image pickup apparatus accordingto claim 43, wherein said reflecting section is shaped like a prismhaving a refracting surface that receives light incident from said lightsource and a reflecting surface that reflects light incident from saidrefracting surface.
 45. The image pickup apparatus according to claim43, wherein the refracting surface of said reflecting section isconstructed of a flat surface whose gradient with respect to the opticalaxis is 4° or less.
 46. The image pickup apparatus according to claim43, wherein the reflecting surface of said reflecting section isconstructed of a flat surface or curved surface.
 47. The image pickupapparatus according to claim 43, wherein a pair or a plurality of pairsof said reflecting sections is provided on both sides of the opticalaxis.
 48. The image pickup apparatus according to claim 43, wherein theshape of said reflecting section is determined in such a way that theirradiation range of light irradiated through said reflecting sectionand the irradiation range of light irradiated through said lens sectionand said reflection member substantially overlap with each other. 49.The image pickup apparatus according to claim 43, wherein an angle αformed by light emitted from the center of said light source andincident on said reflecting section with respect to the optical axis iswithin a range of 20°≦α≦70°.
 50. The image pickup apparatus according toclaim 43, wherein the area of said reflection member covering said frontspace is a surface of second order.
 51. The image pickup apparatusaccording to claim 43, wherein the area of said reflection membercovering said front space is a semi-ellipsoidal curved surface whosefocal point coincides with the center of said light source.
 52. Theimage pickup apparatus according to claim 43, wherein said light sourcehas a cylindrical shape and the lens section of said optical member is acylindrical lens or toric lens having positive refracting power withinthe plane perpendicular to the longitudinal direction of said lightsource.
 53. The image pickup apparatus according to claim 43, having acard type configuration.
 54. The image pickup apparatus according toclaim 43, wherein the irradiation range of light emitted from saidoptical member is made variable by changing a relation of positionsbetween said light source and said optical member in the direction ofthe optical axis.
 55. An image pickup apparatus comprising: a lightsource; an optical member which is placed in front of said light sourceand provided with a lens section having positive refracting power andbeing place on and close to the optical axis on the entrance surfaceside of this optical member; a first reflection member which is placedin such a way as to cover the back of said light source and a frontspace between said light source and said optical member and reflectslight emitted from said light source forward; and a second reflectionmember which is placed to peripheral side of said lens section near theentrance surface of said optical member, provided closer to the opticalaxis than the area through which the light reflected by the part of saidfirst reflection member covering said front space passes, and reflectslight from said light source forward.
 56. The image pickup apparatusaccording to claim 55, wherein said second reflection member isconstructed of a flat surface or curved surface.
 57. The image pickupapparatus according to claim 55, wherein a pair or a plurality of pairsof said second reflection members is provided on both sides of theoptical axis.
 58. The image pickup apparatus according to claim 55,wherein said second reflection member is shaped in such a way that theirradiation range of light irradiated through said second reflectionmember and the irradiation range of light irradiated through said lenssection and said first reflection member substantially overlap with eachother.
 59. The image pickup apparatus according to claim 55, wherein anangle α formed by the light emitted from the center of said light sourceand incident on said second reflection member with respect to theoptical axis is within a range of 20°≦α≦70°.
 60. The image pickupapparatus according to claim 55, wherein said light source has acylindrical shape and the area of said first reflection member coveringthe back of said light source is shaped like a semi-cylinder concentricwith said light source.
 61. The image pickup apparatus according toclaim 55, wherein the area of said first reflection member covering saidfront space is a curved surface of second order.
 62. The image pickupapparatus according to claim 55, wherein the area of said firstreflection member covering said front space is a semi-ellipsoidal curvedsurface whose focal point coincides with the center of said lightsource.
 63. The image pickup apparatus according to claim 55, whereinsaid light source has a cylindrical shape and the lens section of saidoptical member is a cylindrical lens or toric lens having positiverefracting power within the plane perpendicular to the longitudinaldirection of said light source.
 64. The image pickup apparatus accordingto claim 55, having a card type configuration.
 65. The image pickupapparatus according to claim 55, wherein the irradiation range of lightemitted from said optical member and said second reflection member ismade variable by changing a relation of positions between said lightsource, said optical member and said second reflection member in thedirection of the optical axis.